## Swift Vs Python

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# Swift Vs Python

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## Programming Languages: Their popularity

Every passing year witnesses changes in the preferences of programming languages. Some of them get knocked off the perch, while others continue growing. In recent years, two programming languages stand out from the rest and are rapidly growing in popularity. Those two are Swift and Python.

In this article, we will talk about the attributes of Swift and Python, their pros and cons and how they are similar to each other. Read along to know more.

## What they are

Swift and Python. One is a general-purpose, multi-paradigm, object-oriented, functional, imperative and block-structured language while the latter is a widely-used general-purpose, high-level programming language.

Python was originally designed by Guido van Rossum in 1991 and further developed by Python Software Foundation. It was developed to stress code readability along with its syntax enables programmers to code less to express their concepts. It helps coders to speed up the workflow and integrate systems more efficiently. In a survey by Stack Overflow in 2017, Python was the fastest-growing programming language.

This resulted in numerous companies prominently using Python as their programming language, the list including Quora, Netflix, Dropbox, Reddit, Facebook, Spotify, Instagram, etc.

In terms of Python’s usability shown above, Data analysis goes first, followed by web development, machine learning, and DevOps. However, Python is less used for educational purposes, prototyping, and Quality Assurance Services.

Now talking about Swift, it was designed and released in 2014 after conducting fresh research on programming languages and by using a modern approach to safety, software design patterns by Apple Inc. It is a completely new programming language for the iOS application, macOS application, watchOS application, tvOS application. Needless to say, it quickly grew to be one of the top 5 programming languages and became the most used programming language among the Apple developer community within a short span of than 5 years, also effectively replacing the previously used Objective C.

Let us share an important piece of information with you. According to a survey done on the most popular programming languages, Python takes the first spot with overwhelming popularity with a share of 25.36%, whereas Swift is climbing up the ladder at the 9th spot with 2.69% share.

The table is mentioned below:

In this section, we will focus on the criteria that make Python a truly developer-friendly language. As we learnt that Python has its uses in numerous lines of work, we will find out how it ticks the checkboxes of the required criteria.

One of the prime benefits of using Python is that it is simple to code and read. Of course, it is not a repetitive language to follow but is very similar to English and hence is easy to follow. Moreover, Python is a good choice for beginners in programming

It is a programming language that is object-oriented as well as procedural. Its procedural paradigm allows reuse code and object-oriented methodology allows varied inheritances and summarising data and functions as one

• Open-source

As Python is open source, you can download and modify its source code. This versatile feature led to the formation of a strong community that keeps growing stronger

• Integration with other languages

Being an extensible and embeddable language, programmers can easily integrate Python to Java applications, C, and C++

• Portability and compatibility

Python is compatible with various platforms. If required, users do not require to change the code before moving the project. to be moved to another platform

• Vast collection of libraries

Being in the game for a long time, Python boasts having a strong community with a vast range of libraries and frameworks for different purposes. providing programmers with a wide spectrum of opportunities. Additionally, libraries like Pandas, Plotly, NumPy, Pipenv, and others and are included as well. Django, Flask, CherryPy, and PyTorch are.among the most famous frameworks.

With the pros come the cons. There is also the other side of a coin that needs attention. In spite of having a long history in the programming world, Python still has several weak sides.

• Not ideal for Mobile development

Python is not a good solution for mobile developers. However, a come-around solution with a few challenges is Kivy - a cross-platform Python framework for developing mobile apps

• Design restrictions

There are specific design limitations in Python. Being dynamically typed language using duck typing, Python automatically identifies a type of a variable and can cause runtime errors Although it is not frequent, it does make errors at times.

• Memory consumption

Python consumes high memory and is definitely not a good option to run intensive memory tasks.

## Swift pros and cons

Being a relatively new programming language, Swift was launched at the WWDC conference in 2014. According to Apple, the primary features of Swift is that it is fast, modern and interactive. Swift's creator Chris Lattner his creation was a result of ideas inspired by different languages such as C#, Ruby, and especially by Python. That's why we can easily find a couple of similarities between Swift and Python.

Nevertheless, let’s see what the pros and cons of Swift are.

• Easy to read and maintain

The Swift program codes are based on English as it acquired syntaxes from other programming languages, thus making the language more expressive

• Scalable

More features to Swift, so it is a scalable programming language. Swift has already replaced Objective C and Swift is what Apple is relying on

• Concise

Swift does not include long lines of code and that favours the developers who want a concise syntax, thus increasing the development and testing rate of the program

• Safety and improved performance

Almost 40% better than the Objective-C, Swift is handier to tackle the bugs that lead to safer programming when speed and performance is concerned

• Cross-device support

This language can handle a wide range of Apple platforms such as iOS, iOS X, macOS, tvOS, and watchOS

• Automatic Memory Management

This feature prevents memory leaks and helps in optimising the application’s performance that is done by using Automatic Reference Counting.

• Compatibility issues

The updated versions Swift is observed to be a bit unstable with the newer versions of Apple leading to a few issues. Switching to a newer version of Swift is the fix but that is costly

• Speed Issues

This is relevant to the earlier versions of the Swift programming language

• Less in number:

The number of Swift developers is limited as Swift is a new programming language

Developers will be facing delays over their apps written in Swift to be uploaded to the App Store only after iOS 8 and Xcode 6 are released. The estimated time for release is reported to be September-October, 2014.

## Common attributes of Swift and Python

Swift and Python are predominantly contrasting languages. Despite that, the do possess some common traits. Let’s see what they are.

• Both Swift and Python have a distinct syntax and are very similar to the English language. Missing semicolons while coding in either Swift or Python will not result in errors.
• Both languages have a REPL environment that aids in detecting errors in code and debugging
• Both are multi-paradigm programming languages
• They have additional tools to facilitate learning.

## What makes Swift and Python different from each other?

From the previous discussions in this article, it is crystal clear that Swift and Python are fundamentally different from each other. Apple’s Swift is ideal for developing software for the Apple ecosystem while Python can be utilised for use cases but is mainly applied in back-end development. Moreover, as Apple claims, Swift is 8.4x faster than Python in terms of performance.

Choosing between Swift and Python depends on the intent of the programmer. If the purpose is developing mobile applications that need to work flawlessly in the Apple platforms, then Swift is the ultimate choice. However, if the intentions are to develop artificial intelligence, design a prototype or build the backend, then Python is the one.

## In the end, what matters is the intent

So now we see that in fact choosing Python or Swift for coding mostly depends on your purpose. If you are fond of developing mobile applications that will work seamlessly on Apple operating systems, you should definitely choose Swift. Python is good in case you want to develop your own artificial intelligence, build the backend or create a prototype.

There is no hiding the fact that both Swift and Python are good at what they do. While Python has been a game-changer for years, Swift has been rapidly rising up the ranks. Comparing the two directly is a bit unjust as each one of the two has their own uses.

The best person to select the right programming language is you! So be the judge of your decision. Good luck!

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## How to Build a Python GUI Application With wxPython

A Graphical User Interface or GUI is a user interface that includes graphical elements that enable a person to communicate with electronic devices like computers, hand-held devices, and other appliances. It displays information using icons, menus, and graphics. They are handled with the help of a pointing device such as a mouse, trackball or a stylus.A GUI is basically an application that has windows, buttons and lots of other widgets that allows a user to interact with your application. A web browser is a common example of a GUI that has buttons, tabs, and the main window and where the content is displayed.It was developed by the Xerox Palo Alto research laboratory in the late 1970s. Today, every OS has its own GUI. Software applications make use of these and develop their own GUIs.Python contains many GUI toolkits, out which Tkinter, wxPython, and PyQt are the important ones. All these toolkits have the ability to work with Windows, macOS, and Linux with the additional quality of working on mobile phones.How to get started with wxPython?wxPython was first released in the year 1998. It is an open-source cross-platform Python GUI toolkit used as a wrapper class around a C++ library called wxWidgets. The main feature of wxPython which distinguishes itself from other toolkits like PyQt and Tkinter is that it uses actual widgets on the native platform where required. This allows the wxPython applications to look native to the operating system in which it is running.The wxPython toolkit contains a lot of core widgets along with many custom widgets which you can download from the Extra Files section of the wxPython official page.Here, there is a download of the wxPython demo package which is an application demonstrating the robustness of the widgets included with wxPython. The main advantage of this demo is that you can view it one tab and run it in another and it also allows to edit and re-run the code to observe the changes.Installing wxPythonYou will be using the latest wxPython release, wxPython 4, which is also called the wxPython’s Project Phoenix. It is a new implementation of wxPython that aims at improving the speed, maintainability, and extensibility of wxPython. The wxPython 3 and wxPython 2 were built only for Python 2. The maintainer of wxPython rejected a lot of aliases and cleaned up a lot of code to make wxPython more easy and Pythonic.If you are migrating from an older version of wxPython to wxPython 4, take a look at the following references:Classic version vs project PhoenixPhoenix Migration GuideThe Phoenix version is compatible with both Python 2.7 and Python 3. You can use pip to install wxPython 4:$pip install wxpythonYou will get a prerequisites section on the Github page of wxPython which will provide information to install wxPython on Linux systems.You can also look into the Extras Linux section to learn about the Python wheels for both GTK2 and GTK3 versions. To install one of the wheels, use the command below:$ pip install -U -f https://extras.wxpython.org/wxPython4/extras/linux/gtk3/ubuntu-18.04/ wxPythonRemember to modify the command to match with the version of Linux.Components of GUIAs mentioned earlier, GUI is nothing but an interface that allows user interaction.Common components of the user interfaces:Main Window.Menu.Toolbar.Buttons.Text Entry.Labels.These items are generally known as widgets. wxPython supports many other common widgets and many custom widgets that are arranged in a logical manner by a developer to allow user interaction.Event LoopsA GUI works by waiting for the user to perform an action. This is known as an event. An event occurs when something is typed by the user or when the user uses their mouse to press a button or some widget while the application is in focus.The GUI toolkit runs an infinite loop called an event loop underneath the covers. The task of the event loop is to act on occurred events on the basis of what the developer has coded the application to do. The application ignores the event when it is not able to catch it.When you are programming a graphical user interface, make sure to attach the widgets to event handlers in order to make your application do something.You can also block an event loop to make the GUI unresponsive which will appear to freeze to the user. This is a special consideration for you to keep in mind while working with event loops. Launch a special thread or process whenever a GUI takes longer than a quarter of a second to launch a process.The frameworks of wxPython contain special thread-safe methods that you can use to communicate back to your application. This informs the thread is finished or given an update.How to create a Skeleton Application?An application skeleton is basically used for prototyping. It is a user interface comprising of widgets that do not contain event handlers. You just need to create the GUI and show it to the stakeholders for signing off and avoid spending time on the backend logic.An example of creating a Hello World application with Python:import wx   application = wx.App() framework = wx.Frame(parent=None, title='Hello World') framework.Show() app.MainLoop()In the example above, there are two parts of the program – wx.App and wx.Frame. The former one is wxPython’s application object which is basically required for running the GUI. It initiates the .MainLoop() which is the event loop you have learned earlier.The latter part creates a window for user interaction. It informs wxPython that the frame has no parent and its title is Hello World. If you run the code above, this is how it will look like:The application will look different if you execute it in Mac or Linux.Note: Mac users may get the following message: This program needs access to the screen. Please run with a Framework build of Python, and only when you are logged in on the main display of your Mac. If you see this message and you are not running in a virtualenv, then you need to run your application with pythonw instead of python. If you are running wxPython from within a virtualenv, then see the wxPython wiki for the solution.The minimize, maximize and exit will be included in the wx.Frame by default. However, most wxPython code will require you to make the wx.Frame as a subclass and other widgets in order to grab the full power of the toolkit.Let us rewrite the code using class:import wx   class MyFramework(wx.Frame):     def frame(self):         super().frame(parent=None, title='Hello World') self.Show()   if __name__ == '__main__':     application = wx.App()     framework = MyFramework() application.MainLoop()This code can be used as a template for your application.Widgets in wxPythonThe wxPython toolkit allows you to create rich applications from more than one hundred widgets. But it can be very daunting to choose the perfect widget from such a large number, so wxPython has included a wxPython Demo which contains a search filter which will help you to find the right widget from the list.Now, let us add a button and allow the user to enter some text by adding a text field:import wx   class MyFramework(wx.Frame):     def frame(self):         super().frame(parent=None, title='Hello World')         panel = wx.Panel(self)   self.text_ctrl = wx.TextCtrl(panel, pos=(5, 5)) my_button = wx.Button(panel, label='Press Me', pos=(5, 55))   self.Show()   if __name__ == '__main__':     application = wx.App()     framework = MyFramework() application.MainLoop()When you run the code, the application will look like this:The first widget that is recommended on Windows is wx.Panel. It makes the background color of the frame as the right shade of gray. Tab traversal is disabled without a Panel on Windows.If the panel is the sole child of the frame, it will be expanded automatically to fill the frame with itself. The next thing you need to do is to add a wx.TextCtrl to the panel. The first argument is always that which parent the widget should go to for almost all widgets. So if you are willing to keep the text control and the button on the top of the panel, it is the parent you need to specify.You also need to inform wxPython about the position of the widget. You can do it using the pos parameter. The default location is (0,0) which is actually at the upper left corner of the parent. So to change the text control, you can change the position of the frame, you can shift its left corner 5 pixels from the left(x) and 5 pixels from the top(y). Finally, you can add your button to the panel and label it. You can also set the y-coordinate to 55 to prevent the overlapping of widgets.Absolute PositioningAbsolute positioning is the technique found in most GUI toolkits by which you can provide the exact coordinates for your widget’s position.There might be situations when you need to keep track of all your widgets and relocate the widgets in case of a complex application. This can be a really difficult thing to do. However, most modern-day toolkits provide a solution for this, which we’ll study next.Sizers (Dynamic Sizing)Sizers are methods to define the control layout in dialogs in wxPython. They have the ability to create dialogs that are not dependent on the platform. They manage the positioning of the widgets and adjust them when the user resizes the application window.Some of the primary types of sizers that are commonly used are:wx.BoxSizerwx.GridSizerwx.FlexGridSizerAn example code to add wx.BoxSizer to the previous code:import wx   class MyFramework(wx.Frame):     def frame(self):         super().frame(parent=None, title='Hello World')         panel = wx.Panel(self)         my_sizer = wx.BoxSizer(wx.VERTICAL)         self.text_ctrl = wx.TextCtrl(panel) my_sizer.Add(self.text_ctrl, 0, wx.ALL | wx.EXPAND, 5)         my_button = wx.Button(panel, label='Press Me') my_sizer.Add(my_btn, 0, wx.ALL | wx.CENTER, 5)         panel.SetSizer(my_sizer)         self.Show()   if __name__ == '__main__':     application = wx.App()     framework = MyFramework() application.MainLoop() In the example above, an instance of wx.BoxSixer is created and passed to wx.VERTICAL which is actually the orientation that widgets are included in the sizer. The widgets will be added in a vertical manner from top to bottom. You can also set the BoxSizer’s orientation to wx.HORIZONTAL. In this case, the widgets are added from left to right.  You can use .Add() to a widget to a sizer which takes maximum five arguments as follows: window ( the widget )- This is the widget that is added to the sizer. proportion - It sets how much space corresponding to other widgets in the sizer will the widget should take. By default, the proportion is zero which leaves the wxPython to its original proportion. flag - It allows you to pass in multiple flags by separating them with a pipe character: |. The text control is added using wx.ALL and wx.EXPAND flags. The wx.ALL flag adds a border on all sides of the widget. On the other hand, wx.EXPAND expands the widgets as much as the sizer can be expanded. border - This parameter informs wxPython about the number of pixels of border needed around the widget.  userData - It is a rare argument that is used for resizing in case of complex applications. However, in this example, the wx.EXPAND flag is replaced with wx.CENTER to display the button in the center on-screen. When you run the code, your application will look something like this:Adding an event using wxPython Though your application looks cool, but it really does nothing. The button you have created does nothing on pressing it. Let us give the button a job:import wx   class MyFramework(wx.Frame):     def frame(self):         super().frame(parent=None, title='Hello World')         panel = wx.Panel(self)         my_sizer = wx.BoxSizer(wx.VERTICAL)         self.text_ctrl = wx.TextCtrl(panel) my_sizer.Add(self.text_ctrl, 0, wx.ALL | wx.EXPAND, 5)         my_button = wx.Button(panel, label='Press Me') my_button.Bind(wx.EVT_BUTTON, self.on_press) my_sizer.Add(my_btn, 0, wx.ALL | wx.CENTER, 5)         panel.SetSizer(my_sizer)         self.Show()   def button_press(self, event):         value = self.text_ctrl.GetValue()         if not value:             print("You didn't enter anything!")        else:             print(f'You typed: "{value}"')   if __name__ == '__main__':     application = wx.App()     framework = MyFramework() application.MainLoop() You can attach event bindings to the widgets in wxPython. This allows them to respond to certain types of events.If you want the button to do something, you can do it using the button’s .Bind() method. It takes the events you want to bind to, the handler to call an event, an optional source, and a number of optional ids. In the example above, the button object is binded to wx.EVT_BUTTON and told to call button_press when the event gets fired..button_press also accepts a second argument by convention that is called event. The event parameter suggests that the second argument should be an event object.You can get the text control’s contents with the help of GetValue() method within .button_press.How to create a Working Application?Consider a situation where you are asked to create an MP3 tag editor. The foremost thing you need to do is to look out for the required packages.Consider a situation where you are asked to create an MP3 tag editor. The foremost thing you need to do is to look out for the required packages.If you make a Google search for Python mp3 tag editor, you will find several options as below:mp3 -taggereyeD3mutagenOut of these, eyeD3 is a better choice than the other two since it has a pretty nice API that can be used without getting bogged down with MP3’s ID3 specification.You can install eyeD3 using pip from your terminal:pip install eyed3If you want to install eyeD3 in macOS, you have to install libmagic using brew. Linux and Windows users can easily install using the command mentioned above.Designing the User Interface using wxPythonThe very first thing you must do before designing an interface is to sketch out how you think the interface should look.The user interface should perform the following tasks:Open up one or more MP3 files.Display the current MP3 tags.Edit an MP3 tag.If you want to open a file or a folder, you need to have a menu or a button in your user interface. You can do that with a File menu. You will also need a widget to see the tags for multiple MP3 files. A tabular structure consisting of columns and rows would be perfect for this case since you can have labeled columns for the MP3 tags. wxPython toolkit consists of afew widgets to perform this task:wx.grid.Gridwx.ListCtrlwx.ListCtrl would be a better option of these two since the Grid widget is overkill and complex in nature. Finally, you can use a button to perform the editing tasks.Below is an illustration of what the application should look like:Creating the User Interface You can refer to a lot of approaches when you are creating a user interface. You can follow the Model-View-Controller design pattern that is used for developing user interfaces which divides the program logic into three interconnected elements. You should know how to split up classes and how many classes should be included in a single file and so on.However, in this case, you need only two classes which are as follows:wx.Panel classwx.Frame class Let’s start with imports and the panel class:import eyed3 import glob import wx   class Mp3Panel(wx.Panel):     def frame(self, parent):         super().__init__(parent) main_sizer = wx.BoxSizer(wx.VERTICAL) self.row_obj_dict = {}   self.list_ctrl = wx.ListCtrl(             self, size=(-1, 100),               style=wx.LC_REPORT | wx.BORDER_SUNKEN         ) self.list_ctrl.InsertColumn(0, 'Artist', width=140) self.list_ctrl.InsertColumn(1, 'Album', width=140) self.list_ctrl.InsertColumn(2, 'Title', width=200) main_sizer.Add(self.list_ctrl, 0, wx.ALL | wx.EXPAND, 0)         edit_button = wx.Button(self, label='Edit') edit_button.Bind(wx.EVT_BUTTON, self.on_edit) main_sizer.Add(edit_button, 0, wx.ALL | wx.CENTER, 5)         self.SetSizer(main_sizer)   def on_edit(self, event):         print('in on_edit')   def update_mp3_listing(self, folder_path):         print(folder_path)In this example above, the eyed3 package, glob package, and the wx package are imported. Then, the user interface is created by making wx.Panel a subclass. A dictionary row_obj_dict is created for storing data about the MP3s. The next thing you do is create a wx.ListCtrl and set it to report mode, i.e. wx.LC_REPORT. This report flag is the most popular among all but you can also choose your own depending upon the style flag that you pass in. Now you need to call .InsertColumn() to make the ListCtrl have the correct headers and then provide the index of the column, its label and the width of the column pixels. Finally, you need to add your Edit button, an event handler, and a method. The code for the frame is as follows:class Mp3Frame(wx.Frame):     def__init__(self):         super().__init__(parent=None,                          title='Mp3 Tag Editor') self.panel = Mp3Panel(self) self.Show()   if __name__ == '__main__':     app = wx.App(False)     frame = Mp3Frame() app.MainLoop()This class function is a better and simpler approach than the previous one because you just need to set the title of the frame and instantiate the panel class, MP3Panel. The user interface will look like this after all the implementations:The next thing we will do is add a File menu to add MP3s to the application and also edit their tags.Make a Functioning ApplicationThe very first thing you need to do to make your application work is to update the wx.Frame class to include the File menu which will allow you to add MP3 files.Code to add a menu bar to our application:class Mp3Frame(wx.Frame):   def__init__(self):         wx.Frame.__init__(self, parent=None,                             title='Mp3 Tag Editor') self.panel = Mp3Panel(self) self.create_menu() self.Show()   def create_menu(self): menu_bar = wx.MenuBar() file_menu = wx.Menu() open_folder_menu_item = file_menu.Append( wx.ID_ANY, 'Open Folder',   'Open a folder with MP3s'         ) menu_bar.Append(file_menu, '&File') self.Bind(             event=wx.EVT_MENU,               handler=self.on_open_folder,             source=open_folder_menu_item,         ) self.SetMenuBar(menu_bar)   def on_open_folder(self, event):         title = "Choose a directory:" dlg = wx.DirDialog(self, title,                              style=wx.DD_DEFAULT_STYLE) if dlg.ShowModal() == wx.ID_OK:             self.panel.update_mp3_listing(dlg.GetPath()) dlg.Destroy() In the example code above, .create_menu() is called within the class’s constructor and then two instances – wx.MenuBar and wx.Menu are created.Now, if you’re willing to add an item to the menu, you need to call the menu instance’s .Append() and pass the following things:A unique identifierLabelA help stringAfter that call the menubar’s .Append() to add the menu to the menubar. It will take the menu instance and the label for menu. The label is called as &File so that a keyboard shortcut is created to open the File menu using just the keyboard.Now self.Bind() is called to bind the frame to wx.EVT_MENU. This informs wxPython about which handler should be used and which source to bind the handler to. Lastly, call the frame’s .SetMenuBar and pass it the menubar instance. Your menu is now added to the frame.Now let’s come back to the menu item’s event handler:def on_open_folder(self, event):     title = "Choose a directory:" dlg = wx.DirDialog(self, title, style=wx.DD_DEFAULT_STYLE) if dlg.ShowModal() == wx.ID_OK:         self.panel.update_mp3_listing(dlg.GetPath()) dlg.Destroy()You can use wxPython’s wx.DirDialog to choose the directories of the correct MP3 folder. To display the dialog, use .ShowModal(). This will display the dialog modally but will disallow the user to interact with the main application.  You can get to the user’s choice of path using .GetPath() whenever the user presses the OK button. This path has to be added to the panel class and this can be done by the panel’s .update_mp3_listing().Finally, you will have to close the dialog and the best method is using .Destroy().  There are methods to close the dialog like .Close() which will just dialog but will not destroy it, so .Destroy() is the most effective option to prevent such situation.Now let’s update the MP3Panel class starting with .update_mp3_listing():def update_mp3_listing(self, folder_path): self.current_folder_path = folder_path self.list_ctrl.ClearAll()   self.list_ctrl.InsertColumn(0, 'Artist', width=140) self.list_ctrl.InsertColumn(1, 'Album', width=140) self.list_ctrl.InsertColumn(2, 'Title', width=200) self.list_ctrl.InsertColumn(3, 'Year', width=200)       mp3s = glob.glob(folder_path + '/*.mp3')     mp3_objects = []     index = 0 for mp3 in mp3s:         mp3_object = eyed3.load(mp3) self.list_ctrl.InsertItem(index,               mp3_object.tag.artist) self.list_ctrl.SetItem(index, 1,               mp3_object.tag.album) self.list_ctrl.SetItem(index, 2,               mp3_object.tag.title)         mp3_objects.append(mp3_object) self.row_obj_dict[index] = mp3_object         index += 1In the example above, the current directory is set to the specified folder and the list control is cleared. The list controls stay fresh and shows the MP3s you’re currently working with. Next, the folder is taken and Python’s globmoduleis used to search for the MP3 files. Then, the MP3s are looped over and converted into eyed3 objects. This is done by calling the .load() of eyed3. After that, you can add the artist, album, and the title of the Mp3 to the control list given that the MP3s have the appropriate tags..InsertItem() is used to add a new row to a list control for the first time and SetItem()  is used to add rows to the subsequent columns. The last step is to save your MP3 object to your Python dictionary row_obj_dict.Now to edit an MP3’s tags, you need to update the .on_edit() event handler:def on_edit(self, event):     selection = self.list_ctrl.GetFocusedItem() if selection >= 0:         mp3 = self.row_obj_dict[selection] dlg = EditDialog(mp3) dlg.ShowModal()         self.update_mp3_listing(self.current_folder_path) dlg.Destroy()The user’s selection is taken by calling the list control’s .GetFocusedItem(). It will return -1 if the user will not select anything in the list control. However, if you want to extract the MP3 obj3ct from the dictionary, the user have to select something. You can then open the MP3 tag editor dialog which will be a custom dialog. As before, the dialog is shown modally, then the last two lines in .on_edit() will execute what will eventually display the current MP3 tag information. SummaryLet us sum up what we have learned in this article so far – Installing wxPython and Working with wxPython’s widgets Working of events in wxPython Comparing absolute positioning with sizers Creating a skeleton application and a working application The main feature of the wxPython Graphical User Interface is its robustness and a large collection of widgets that you can use to build cross-platform applications. Since you have now learned how to create a working application, that is an MP3 tag editor, you can try your hand to enhance this application to a more beautiful one with lots of new features or you can perhaps create your own wonderful application. To gain more knowledge about Python tips and tricks, check our Python tutorial and get a good hold over coding in Python by joining the Python certification course.
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How to Build a Python GUI Application With wxPytho...

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The Python Standard Library comprises of sophisticated and robust capabilities for working with larger packages. You will find modules for working with sockets and with files and file paths.Though there might be great packages that Python comes with, there are more exciting and fantastic projects outside the standard library which are mostly called the Python Packaging Index (PyPI). It is nothing but a repository of software for the Python programming language.The PyPI package is considered as an important property for Python being a powerful language. You can get access to thousands of libraries starting from Hello World to advanced deep learning libraries.What is PyPI"PyPI" should be pronounced like "pie pea eye", specifically with the "PI" pronounced as individual letters, but rather as a single sound. This minimizes confusion with the PyPy project, which is a popular alternative implementation of the Python language.The Python Package Index, abbreviated as PyPI is also known as the Cheese Shop. It is the official third-party software repository for Python, just like CPAN is the repository for  Perl.  Some package managers such as pip, use PyPI as the default source for packages and their dependencies. More than 113,000 Python packages can be accessed through PyPI.How to use PyPITo install the packages from PyPI you would need a package installer. The recommended package installer for PyPI is ‘pip’. Pip is installed along when you install Python on your system. To learn more about ‘pip’, you may go through our article on “What is pip”. The pip command is a tool for installing and managing Python packages, such as those found in the Python Package Index. It is a replacement for easy_install.To install a package from the Python Package Index, just open up your terminal and type in a search query using the PIP tool. The most common usage for pip is to install, upgrade or uninstall a package. Starting with a Small Python PackageWe will start with a small Python package that we will use as an example to publish to PyPI. You can get the full source code from the GitHub repository. The package is called reader and it is an application by which you can download and read articles. Below shows the directory structure of reader :reader/  │  ├── reader/  │   ├── config.txt  │   ├── feed.py  │   ├── __init__.py  │   ├── __main__.py  │   └── viewer.py  │  ├── tests/  │   ├── test_feed.py  │   └── test_viewer.py  │  ├── MANIFEST.in  ├── README.md  └── setup.py The source code of the package is in a reader subdirectory that is bound with a configuration file. The GitHub repository also contains few tests in a separate subdirectory. In the coming sections, we will discuss the working of the reader package and also take a look at the special files which include setup.py, README.md, MANIFEST.in, and others. Using the Article ReaderThe reader is a primitive data format used for providing users with the latest updated content. You can download the frequent articles from the article feed with the help of reader. You can get the list of articles using the reader:$python -m reader The latest tutorials from Real Python (https://realpython.com/) 0 How to Publish an Open-Source Python Package to PyPI 1 Python "while" Loops (Indefinite Iteration) 2 Writing Comments in Python (Guide) 3 Setting Up Python for Machine Learning on Windows 4 Python Community Interview With Michael Kennedy 5 Practical Text Classification With Python and Keras 6 Getting Started With Testing in Python 7 Python, Boto3, and AWS S3: Demystified 8 Python's range() Function (Guide) 9 Python Community Interview With Mike Grouchy 10 How to Round Numbers in Python 11 Building and Documenting Python REST APIs With Flask and Connexion – Part 2 12 Splitting, Concatenating, and Joining Strings in Python 13 Image Segmentation Using Color Spaces in OpenCV + Python 14 Python Community Interview With Mahdi Yusuf 15 Absolute vs Relative Imports in Python 16 Top 10 Must-Watch PyCon Talks 17 Logging in Python 18 The Best Python Books 19 Conditional Statements in PythonThe articles in the list are numbered. So if you want to read a particular article, you can just write the same command along with the number of the article you desire to read.For reading the article on “How to Publish an Open-Source Python Package to PyPI”, just add the serial number of the article:$ python -m reader 0  # How to Publish an Open-Source Python Package to PyPI  Python is famous for coming with batteries included. Sophisticated  capabilities are available in the standard library. You can find modules  for working with sockets, parsing CSV, JSON, and XML files, and  working with files and file paths. However great the packages included with Python are, there are many  fantastic projects available outside the standard library. These are  most often hosted at the Python Packaging Index (PyPI), historically  known as the Cheese Shop. At PyPI, you can find everything from Hello  World to advanced deep learning libraries.  ...  ...  ...You can read any of the articles in the list just by changing the article number with the command. Quick LookThe package comprises of five files which are the working hands of the reader. Let us understand the implementations one by one: config.txt -  It is a text configuration file that specifies the URL of the feed of articles. The configparser standard library is able to read the text file. This type of file contains key-value pairs that are distributed into different sections.  # config.txt [feed] url=https://realpython.com/atom.xml__main__.py - It is the entry point of your program whose duty is to control the main flow of the program. The double underscores denote the specialty of this file. Python executes the contents of the __main__.py file. # __main__.py from configparser import ConfigParser  from importlib import resources  import sys from reader import feed  from reader import viewer def main(): # Read URL of the Real Python feed from config file  configure=ConfigParser() configure.read_string(resources.readtext("reader","config.txt"))  URL=configure.get("feed","url") # If an article ID is given, show the article  if len(sys.argv) > 1:  article = feed.getarticle(URL, sys.argv[1])  viewer.show(article) # If no ID is given, show a list of all articles else: site = feed.getsite(URL)  titles = feed.gettitles(URL)  viewer.showlist(site,titles)  if __name__ == "__main__": main() __init__.py - It is also considered a special file because of the double underscore. It denotes the root of your package in which you can keep your package constants, your documentations and so on. # __init__.py # Version of the realpython-reader package  __version__= "1.0.0"__version__ is a special variable in Python used for adding numbers to your package which was introduced in PEP 396. The variables which are defined in __init__.py are available as variables in the namespace also. >>> import reader >>> reader.__version__ '1.0.0'feed.py - In the __main__.py, you can see two modules feed and viewer are imported which perform the actual work. The file feed.py  is used to read from a web feed and parse the result.  # feed.py import feedparser import html2text Cached_Feeds = dict() def _feed(url):  """Only read a feed once, by caching its contents""" if url not in _CACHED_FEEDS: Cached_Feeds[url]=feedparser.parse(url) return Cached_Feeds[url]viewer.py -  This file module contains two functions show() and show_list(). # viewer.py def show(article):  """Show one article""" print(article) def show_list(site,titles):  """Show list of articles""" print(f"The latest tutorials from {site}") for article_id,title in enumerate(titles): print(f"{article_id:>3}{title}")The function of show() is to print one article to the console. On the other hand, show_list prints a list of titles.Calling a Package You need to understand which file you should call to run the reader in cases where your package consists of four different source code files. The Python interpreter consists of an -m option that helps in specifying a module name instead of a file name.An example to execute two commands with a script hello.py:$python hello.py Hi there!$ python -m hello Hi there!The two commands above are equivalent. However, the latter one with -m has an advantage. You can also call Python built-in modules with the help of it: $python -m antigravity Created new window in existing browser session.The -m option also allows you to work with packages and modules:$ python -m reader ...The reader only refers to the directory. Python looks out for the file named __main__.py, if the file is found, it is executed otherwise an error message is printed: $python -m math python: No code object available for mathPreparing Your PackageSince now you have got your package, let us understand the necessary steps that are needed to be done before the uploading process. Naming the Package Finding a good and unique name for your package is the first and one of the most difficult tasks. PyPI has more than 150,000 packages already in their list, so chances are that your favorite name might be already taken. You need to perform some research work in order to find a perfect name. You can also use the PyPI search to verify whether it is already used or not. We will be using a more descriptive name and call it realpython-reader so that the reader package can be easily found on PyPI and then use it to install the package using pip:$ pip install realpython-readerHowever, the name we have given is realpython-reader but when we import it, it is still called as reader:>>> import reader >>> help(reader) >>> from reader import feed >>> feed.get_titles() ['How to Publish an Open-Source Python Package to PyPI', ...]You can use a variety of names for your package while importing on PyPI but it is suggested to use the same name or similar ones for better understanding. Configuring your PackageYour package should be included with some basic information which will be in the form of a setup.py file. The setup.py is the only fully supported way of providing information, though Python consists of initiatives that are used to simplify this collection of information.The setup.py file should be placed in the top folder of your package. An example of a setup.py  for reader: import pathlib from setuptools import setup # The directory containing this file HERE = pathlib.Path(__file__).parent # The text of the README file README = (HERE/"README.md").read_text() # This call to setup() does all the work setup( name="realpython-reader",  version="1.0.1",  descp="The latest Python tutorials",  long_descp=README, long_descp_content="text/markdown",  URL="https://github.com/realpython/reader",  author="Real Python",  authoremail="office@realpython.com",  license="MIT",  classifiers=[  "License :: OSI Approved :: MIT License",  "Programming Language :: Python :: 3",  "Programming Language :: Python :: 3.7",  ],  packages=["reader"],  includepackagedata=True,  installrequires=["feedparser","html2text"],  entrypoints={  "console_scripts":[  "realpython=reader.__main__:main",  ]  },  ) The necessary parameters available in setuptools in the call to setup() are as follows: name - The name of your package as being appeared on PyPI version - the present version of your package packages - the packages and subpackages which contain your source code You will also have to specify any subpackages if included. setuptools contains find_packages() whose job is to discover all your subpackages. You can also use it in the reader project:from setuptools import find_packages,setup  setup(  ... packages=find_packages(exclude=("tests",)), ... ) You can also add more information along with name, version, and packages which will make it easier to find on PyPI.Two more important parameters of  setup() : install_requires - It lists the dependencies your package has to the third-party libraries. feedparser and html2text are listed since they are the dependencies of reader.entry_points - It creates scripts to call a function within your package. Our script realpython calls the main() within the reader/__main__.py file.Documenting Your PackageDocumenting your package before releasing it is an important step. It can be a simple README file or a complete tutorial webpage like galleries or an API reference.  At least a README file with your project should be included at a minimum which should give a quick description of your package and also inform about the installation process and how to use it. In other words, you need to include your README as the long_descp argument to setup() which will eventually be displayed on PyPI. PyPI uses Markdown for package documentation. You can use the setup() parameter long_description_content_type to get the PyPI format you are working with. When you are working with bigger projects and want to add more documentation to your package, you can take the help of websites like GitHub and Read the Docs. Versioning Your Package Similarly like documentation, you need to add a version to your package. PyPI promises reproducibility by allowing a user to do one upload of a particular version for a package. If there are two systems with the same version of a package, it will behave in an exact manner. PEP 440 of Python provides a number of schemes for software versioning. However, for a simple project, let us stick to a simple versioning scheme. A simple versioning technique is semantic versioning which has three components namely MAJOR, MINOR, and PATCH and some simple rules about the incrementation process of each component: Increment the MAJOR version when you make incompatible API changes. Increment the MINOR version when you add functionality in a backward-compatible manner. Increment the PATCH version when you make backward-compatible bug fixes. (Source) You need to specify the different files inside your project. Also, if you want to verify whether the version numbers are consistent or not, you can do it using a tool called Bumpversion: $pip install bumpversionAdding Files To Your PackageYour package might include other files other than source code files like data files, binaries, documentation and configuration files. In order to add such files, we will use a manifest file. In most cases, setup() creates a manifest that includes all code files as well as README files. However, if you want to change the manifest, you can create a manifest template of your own. The file should be called MANIFEST.in and it will specify rules for what needs to be included and what needs to be excluded: include reader/*.txtThis will add all the .txt files in the reader directory. Other than creating the manifest, the non-code files also need to be copied. This can be done by setting the include_package_data toTrue: setup( ... include_package_data=True, ... )Publishing to PyPI For publishing your package to the real world, you need to first start with registering yourself on PyPI and also on TestPyPI, which is useful because you can give a trial of the publishing process without any further consequences. You will have to use a tool called Twine to upload your package ton PyPI:$ pip install twineBuilding Your PackageThe packages on PyPI are wrapped into distribution packages, out of which the most common are source archives and Python wheels. A source archive comprises of your source code and other corresponding support files wrapped into one tar file. On the other hand, a Python wheel is a zip archive that also contains your code. However, the wheel can work with any extensions, unlike source archives. Run the following command in order to create a source archive and a wheel for your package: $python setup.py sdist bdist_wheelThe command above will create two files in a newly created directory called dist, a source archive and a wheel: reader/ │ └── dist/ ├── realpython_reader-1.0.0-py3-none-any.whl └── realpython-reader-1.0.0.tar.gz The command-line arguments like the sdist and bdist_wheel arguments are all implemented int the upstream distutils standard library. Using the --help-commands option, you list all the available arguments:$ python setup.py --help-commands  Standard commands:    build             build everything needed to install    build_py          "build" pure Python modules (copy to build directory)    < ... many more commands ...>Testing Your Package In order to test your package, you need to check whether the distribution packages you have newly created contain the expected files. You also need to list the contents of the tar source archive on Linux and macOS platforms: $tar tzf realpython-reader-1.0.0.tar.gz realpython-reader-1.0.0/ realpython-reader-1.0.0/setup.cfg realpython-reader-1.0.0/README.md realpython-reader-1.0.0/reader/ realpython-reader-1.0.0/reader/feed.py realpython-reader-1.0.0/reader/__init__.py realpython-reader-1.0.0/reader/viewer.py realpython-reader-1.0.0/reader/__main__.py realpython-reader-1.0.0/reader/config.txt realpython-reader-1.0.0/PKG-INFO realpython-reader-1.0.0/setup.py realpython-reader-1.0.0/MANIFEST.in realpython-reader-1.0.0/realpython_reader.egg-info/ realpython-reader-1.0.0/realpython_reader.egg-info/SOURCES.txt realpython-reader-1.0.0/realpython_reader.egg-info/requires.txt realpython-reader-1.0.0/realpython_reader.egg-info/dependency_links.txt realpython-reader-1.0.0/realpython_reader.egg-info/PKG-INFO realpython-reader-1.0.0/realpython_reader.egg-info/entry_points.txt realpython-reader-1.0.0/realpython_reader.egg-info/top_level.txt On Windows, you can make use of the utility tool 7-zip to look inside the corresponding zip file. You should make sure that all the subpackages and supporting files are included in your package along with all the source code files as well as the newly built files. You can also run twine check on the files created in dist to check if your package description will render properly on PyPI:$ twine check dist/* Checking distribution dist/realpython_reader-1.0.0-py3-none-any.whl: Passed  Checking distribution dist/realpython-reader-1.0.0.tar.gz: Passed Uploading Your PackageNow you have reached the final step,i.e. Uploading your package to PyPI. Make sure you upload your package first to TestPyPI to check whether it is working according to your expectation and then use the Twine tool and instruct it to upload your newly created distribution: $twine upload --repository-url https://test.pypi.org/legacy/ dist/* After the uploading process is over, you can again go to TestPyPI and look at your project being displayed among the new releases. However, if you have your own package to publish, the command is short:$ twine upload dist/* Give your username and password and it’s done. Your package has been published on PyPI. To look up your package, you can either search it or look at the Your projects page or you can just directly go to the URL of your project: pypi.org/project/your-package-name/. After completing the publishing process, you can download it in your system using pip: $pip install your-package-nameMiscellaneous Tools There are some useful tools that are good to know when creating and publishing Python packages. Some of these are mentioned below. Virtual Environments Each virtual environment has its own Python binary and can also have its own set of installed Python packages in its directories. These packages are independent in nature. Virtual environments are useful in situations where there are a variety of requirements and dependencies while working with different projects. You can grab more information about virtual environments in the following references: Python Virtual Environments Pipenv It is recommended to check your package inside a basic virtual environment so that to make sure all necessary dependencies in your setup.py file are included. Cookiecutter Cookiecutter sets up your project by asking a few questions based on a template. Python contains many different templates. Install Cookiecutter using pip:$ pip install cookiecutterTo understand cookiecutter, we will use a template called pypackage-minimal. If you want to use a template, provide the link of the template to the cookiecutter: cookiecutter https://github.com/kragniz/cookiecutter-pypackage-minimal author_name [Louis Taylor]: Real Python author_email [louis@kragniz.eu]: office@realpython.com package_name [cookiecutter_pypackage_minimal]: realpython-reader package_version [0.1.0]: package_description [...]: Read Real Python tutorials package_url [...]: https://github.com/realpython/reader readme_pypi_badge [True]: readme_travis_badge [True]: False readme_travis_url [...]: Cookiecutter sets up your project after you have set up answered a series of questions. The template above will create the following files and directories: realpython-reader/ │ ├── realpython-reader/ │ └── __init__.py │ ├── tests/ │ ├── __init__.py │ └── test_sample.py │ ├── README.rst ├── setup.py └── tox.ini You can also take a look at the documentation of cookiecutter for all the available cookiecutters and how to create your own template. Summary Let us sum up the necessary steps we have learned in this article so far to publish your own package - Finding a good and unique name for your packageConfiguring your package using setup.py Building your package Publishing your package to PyPI Moreover, you have also learned to use a few new tools that help in simplifying the process of publishing packages. You can reach out to Python’s Packaging Authority for more detailed and comprehensive information. To gain more knowledge about Python tips and tricks, check our Python tutorial and get a good hold over coding in Python by joining the Python certification course. Rated 4.5/5 based on 34 customer reviews 12092 What is PyPI & How To Publish An Open-Source P... The Python Standard Library comprises of sophistic... Read More ## How to Round Numbers in Python While you are dealing with data, sometimes you may come across a biased dataset. In statistics, bias is whereby the expected value of the results differs from the true underlying quantitative parameter being estimated. Working with such data can be dangerous and can lead you to incorrect conclusions. To learn more about various other concepts of Python, go through our Python Tutorials or enroll to our Python Certification course online.There are many types of biases such as selection bias, reporting bias, sampling bias and so on. Similarly, rounding bias is related to numeric data. In this article we will see:Why is it important to know the ways to round numbersHow to use various strategies to round numbersHow data is affected by rounding itHow to use NumPy arrays and Pandas DataFrames to round numbersLet us first learn about Python’s built-in rounding process.About Python’s Built-in round() FunctionPython Programming offers a built-in round() function which rounds off a number to the given number of digits and makes rounding of numbers easier. The function round() accepts two numeric arguments, n and n digits and then returns the number n after rounding it to ndigits. If the number of digits are not provided for round off, the function rounds off the number n to the nearest integer.Suppose, you want to round off a number, say 4.5. It will be rounded to the nearest whole number which is 5. However, the number 4.74 will be rounded to one decimal place to give 4.7.It is important to quickly and readily round numbers while you are working with floats which have many decimal places. The inbuilt Python function round() makes it simple and easy.Syntaxround(number, number of digits)The parameters in the round() function are:number - number to be roundednumber of digits (Optional) - number of digits up to which the given number is to be rounded.The second parameter is optional. In case, if it is missing then round() function returns:For an integer, 12, it rounds off to 12For a decimal number, if the last digit after the decimal point is >=5 it will round off to the next whole number, and if =5 print(round(5.476, 2)) # when the (ndigit+1)th digit is 1 print(round("x", 2)) TypeError: type str doesn't define __round__ methodAnother example,print(round(1.5)) print(round(2)) print(round(2.5))The output will be:2 2 2The function round() rounds 1.5 up to 2, and 2.5 down to 2. This is not a bug, the round() function behaves this way. In this article you will learn a few other ways to round a number. Let us look at the variety of methods to round a number.Diverse Methods for RoundingThere are many ways to round a number with its own advantages and disadvantages. Here we will learn some of the techniques to rounding a number.TruncationTruncation, as the name means to shorten things. It is one of the simplest methods to round a number which involves truncating a number to a given number of digits. In this method, each digit after a given position is replaced with 0. Let us look into some examples.ValueTruncated ToResult19.345Tens place1019.345Ones place1919.345Tenths place19.319.345Hundredths place19.34The truncate() function can be used for positive as well as negative numbers:>>> truncate(19.5) 19.0 >>> truncate(-2.852, 1) -2.8 >>> truncate(2.825, 2) 2.82The truncate() function can also be used to truncate digits towards the left of the decimal point by passing a negative number.>>> truncate(235.7, -1) 230.0 >>> truncate(-1936.37, -3) -1000.0When a positive number is truncated, we are basically rounding it down. Similarly, when we truncate a negative number, the number is rounded up. Let us look at the various rounding methods.Rounding UpThere is another strategy called “rounding up” where a number is rounded up to a specified number of digits. For example:ValueRound Up ToResult12.345Tens place2018.345Ones place1918.345Tenths place18.418.345Hundredths place18.35The term ceiling is used in mathematics to explain the nearest integer which is greater than or equal to a particular given number. In Python, for “rounding up” we use two functions namely,ceil() function, andmath() functionA non-integer number lies between two consecutive integers. For example, considering a number 5.2, this will lie between 4 and 5. Here, ceiling is the higher endpoint of the interval, whereas floor is the lower one. Therefore, ceiling of 5.2 is 5, and floor of 5.2 is 4. However, the ceiling of 5 is 5.In Python, the function to implement the ceiling function is the math.ceil() function. It always returns the closest integer which is greater than or equal to its input.>>> import math >>> math.ceil(5.2) 6 >>> math.ceil(5) 5 >>> math.ceil(-0.5) 0If you notice you will see that the ceiling of -0.5 is 0, and not -1.Let us look into a short code to implement the “rounding up” strategy using round_up() function:def round_up(n, decimals=0): multiplier = 10 ** decimals return math.ceil(n * multiplier) / multiplierLet’s look at how round_up() function works with various inputs:>>> round_up(3.1) 4.0 >>> round_up(3.23, 1) 3.3 >>> round_up(3.543, 2) 3.55You can pass negative values to decimals, just like we did in truncation.>>> round_up(32.45, -1) 40.0 >>> round_up(3352, -2) 3400You can follow the diagram below to understand round up and round down. Round up to the right and down to the left.Rounding up always rounds a number to the right on the number line, and rounding down always rounds a number to the left on the number line.Rounding DownSimilar to rounding up we have another strategy called rounding down whereValueRounded Down ToResult19.345Tens place1019.345Ones place1919.345Tenths place19.319.345Hundredths place19.34In Python, rounding down can be implemented using a similar algorithm as we truncate or round up. Firstly you will have to shift the decimal point and then round an integer. Lastly shift the decimal point back.math.ceil() is used to round up to the ceiling of the number once the decimal point is shifted. For “rounding down” we first need to round the floor of the number once the decimal point is shifted.>>> math.floor(1.2) 1 >>> math.floor(-0.5) -1Here’s the definition of round_down():def round_down(n, decimals=0): multiplier = 10 ** decimals return math.floor(n * multiplier) / multiplierThis is quite similar to round_up() function. Here we are using math.floor() instead of math.ceil().>>> round_down(1.5) 1 >>> round_down(1.48, 1) 1.4 >>> round_down(-0.5) -1Rounding a number up or down has extreme effects in a large dataset. After rounding up or down, you can actually remove a lot of precision as well as alter computations.Rounding Half UpThe “rounding half up” strategy rounds every number to the nearest number with the specified precision, and breaks ties by rounding up. Here are some examples:ValueRound Half Up ToResult19.825Tens place1019.825Ones place2019.825Tenths place19.819.825Hundredths place19.83In Python, rounding half up strategy can be implemented by shifting the decimal point to the right by the desired number of places. In this case you will have to determine whether the digit after the shifted decimal point is less than or greater than equal to 5.You can add 0.5 to the value which is shifted and then round it down with the math.floor() function.def round_half_up(n, decimals=0): multiplier = 10 ** decimals return math.floor(n*multiplier + 0.5) / multiplierIf you notice you might see that round_half_up() looks similar to round_down. The only difference is to add 0.5 after shifting the decimal point so that the result of rounding down matches with the expected value.>>> round_half_up(19.23, 1) 19.2 >>> round_half_up(19.28, 1) 19.3 >>> round_half_up(19.25, 1) 19.3Rounding Half DownIn this method of rounding, it rounds to the nearest number similarly like “rounding half up” method, the difference is that it breaks ties by rounding to the lesser of the two numbers. Here are some examples:ValueRound Half Down ToResult16.825Tens place1716.825Ones place1716.825Tenths place16.816.825Hundredths place16.82In Python, “rounding half down” strategy can be implemented by replacing math.floor() in the round_half_up() function with math.ceil() and then by subtracting 0.5 instead of adding:def round_half_down(n, decimals=0): multiplier = 10 ** decimals return math.ceil(n*multiplier - 0.5) / multiplierLet us look into some test cases.>>> round_half_down(1.5) 1.0 >>> round_half_down(-1.5) -2.0 >>> round_half_down(2.25, 1) 2.2In general there are no bias for both round_half_up() and round_half_down(). However, rounding of data with more number of ties results in bias. Let us consider an example to understand better.>>> data = [-2.15, 1.45, 4.35, -12.75]Let us compute the mean of these numbers:>>> statistics.mean(data) -2.275Now let us compute the mean on the data after rounding to one decimal place with round_half_up() and round_half_down():>>> rhu_data = [round_half_up(n, 1) for n in data] >>> statistics.mean(rhu_data) -2.2249999999999996 >>> rhd_data = [round_half_down(n, 1) for n in data] >>> statistics.mean(rhd_data) -2.325The round_half_up() function results in a round towards positive infinity bias, and round_half_down() results in a round towards negative infinity bias.Rounding Half Away From ZeroIf you have noticed carefully while going through round_half_up() and round_half_down(), neither of the two is symmetric around zero:>>> round_half_up(1.5) 2.0 >>> round_half_up(-1.5) -1.0 >>> round_half_down(1.5) 1.0 >>> round_half_down(-1.5) -2.0In order to introduce symmetry, you can always round a tie away from zero. The table mentioned below illustrates it clearly:ValueRound Half Away From Zero ToResult16.25Tens place2016.25Ones place1616.25Tenths place16.3-16.25Tens place-20-16.25Ones place-16-16.25Tenths place-16.3The implementation of “rounding half away from zero” strategy on a number n is very simple. All you need to do is start as usual by shifting the decimal point to the right a given number of places and then notice the digit d immediately to the right of the decimal place in this new number. Here, there are four cases to consider:If n is positive and d >= 5, round upIf n is positive and d < 5, round downIf n is negative and d >= 5, round downIf n is negative and d < 5, round upAfter rounding as per the rules mentioned above, you can shift the decimal place back to the left.There is a question which might come to your mind - How do you handle situations where the number of positive and negative ties are drastically different? The answer to this question brings us full circle to the function that deceived us at the beginning of this article: Python’s built-in round() function.Rounding Half To EvenThere is a way to mitigate rounding bias while you are rounding values in a dataset. You can simply round ties to the nearest even number at the desired precision. Let us look at some examples:ValueRound Half To Even ToResult16.255Tens place2016.255Ones place1616.255Tenths place16.216.255Hundredths place16.26To prove that round() really does round to even, let us try on a few different values:>>> round(4.5) 4 >>> round(3.5) 4 >>> round(1.75, 1) 1.8 >>> round(1.65, 1) 1.6The Decimal ClassThe decimal module in Python is one of those features of the language which you might not be aware of if you have just started learning Python. Decimal “is based on a floating-point model which was designed with people in mind, and necessarily has a paramount guiding principle – computers must provide an arithmetic that works in the same way as the arithmetic that people learn at school.” – except from the decimal arithmetic specification. Some of the benefits of the decimal module are mentioned below -Exact decimal representation: 0.1 is actually 0.1, and 0.1 + 0.1 + 0.1 - 0.3 returns 0, as expected.Preservation of significant digits: When you add 1.50 and 2.30, the result is 3.80 with the trailing zero maintained to indicate significance.User-alterable precision: The default precision of the decimal module is twenty-eight digits, but this value can be altered by the user to match the problem at hand.Let us see how rounding works in the decimal module.>>> import decimal >>> decimal.getcontext() Context( prec=28, rounding=ROUND_HALF_EVEN, Emin=-999999, Emax=999999, capitals=1, clamp=0, flags=[], traps=[ InvalidOperation, DivisionByZero, Overflow ] )The function decimal.getcontext() returns a context object which represents the default context of the decimal module. It also includes the default precision and the default rounding strategy.In the above example, you will see that the default rounding strategy for the decimal module is ROUND_HALF_EVEN. It allows to align with the built-in round() functionLet us create a new Decimal instance by passing a string containing the desired value and declare a number using the decimal module’s Decimal class.>>> from decimal import Decimal >>> Decimal("0.1") Decimal('0.1')You may create a Decimal instance from a floating-point number but in that case, a floating-point representation error will be introduced. For example, this is what happens when you create a Decimal instance from the floating-point number 0.1>>> Decimal(0.1) Decimal('0.1000000000000000055511151231257827021181583404541015625')You may create Decimal instances from strings containing the decimal numbers you need in order to maintain exact precision.Rounding a Decimal using the .quantize() method:>>> Decimal("1.85").quantize(Decimal("1.0")) Decimal('1.8')The Decimal("1.0") argument in .quantize() allows to determine the number of decimal places in order to round the number. As 1.0 has one decimal place, the number 1.85 rounds to a single decimal place. Rounding half to even is the default strategy, hence the result is 1.8.Decimal class:>>> Decimal("2.775").quantize(Decimal("1.00")) Decimal('2.78')Decimal module provides another benefit. After performing arithmetic the rounding is taken care of automatically and also the significant digits are preserved.>>> decimal.getcontext().prec = 2 >>> Decimal("2.23") + Decimal("1.12") Decimal('3.4')To change the default rounding strategy, you can set the decimal.getcontect().rounding property to any one of several flags. The following table summarizes these flags and which rounding strategy they implement:FlagRounding Strategydecimal.ROUND_CEILINGRounding updecimal.ROUND_FLOORRounding downdecimal.ROUND_DOWNTruncationdecimal.ROUND_UPRounding away from zerodecimal.ROUND_HALF_UPRounding half away from zerodecimal.ROUND_HALF_DOWNRounding half towards zerodecimal.ROUND_HALF_EVENRounding half to evendecimal.ROUND_05UPRounding up and rounding towards zeroRounding NumPy ArraysIn Data Science and scientific computation, most of the times we store data as a NumPy array. One of the most powerful features of NumPy is the use of vectorization and broadcasting to apply operations to an entire array at once instead of one element at a time.Let’s generate some data by creating a 3×4 NumPy array of pseudo-random numbers:>>> import numpy as np >>> np.random.seed(444) >>> data = np.random.randn(3, 4) >>> data array([[ 0.35743992, 0.3775384 , 1.38233789, 1.17554883], [-0.9392757 , -1.14315015, -0.54243951, -0.54870808], [ 0.20851975, 0.21268956, 1.26802054, -0.80730293]])Here, first we seed the np.random module to reproduce the output easily. Then a 3×4 NumPy array of floating-point numbers is created with np.random.randn().Do not forget to install pip3 before executing the code mentioned above. If you are using Anaconda you are good to go.To round all of the values in the data array, pass data as the argument to the np.around() function. The desired number of decimal places is set with the decimals keyword argument. In this case, round half to even strategy is used similar to Python’s built-in round() function.To round the data in your array to integers, NumPy offers several options which are mentioned below:numpy.ceil()numpy.floor()numpy.trunc()numpy.rint()The np.ceil() function rounds every value in the array to the nearest integer greater than or equal to the original value:>>> np.ceil(data) array([[ 1., 1., 2., 2.], [-0., -1., -0., -0.], [ 1., 1., 2., -0.]])Look at the code carefully, we have a new number! Negative zero! Let us now take a look at Pandas library, widely used in Data Science with Python.Rounding Pandas Series and DataFramePandas has been a game-changer for data analytics and data science. The two main data structures in Pandas are Dataframe and Series. Dataframe works like an Excel spreadsheet whereas you can consider Series to be columns in a spreadsheet. Series.round() and DataFrame.round() methods. Let us look at an example.Do not forget to install pip3 before executing the code mentioned above. If you are using Anaconda you are good to go.>>> import pandas as pd >>> # Re-seed np.random if you closed your REPL since the last example >>> np.random.seed(444) >>> series = pd.Series(np.random.randn(4)) >>> series 0 0.357440 1 0.377538 2 1.382338 3 1.175549 dtype: float64 >>> series.round(2) 0 0.36 1 0.38 2 1.38 3 1.18 dtype: float64 >>> df = pd.DataFrame(np.random.randn(3, 3), columns=["A", "B", "C"]) >>> df A B C 0 -0.939276 -1.143150 -0.542440 1 -0.548708 0.208520 0.212690 2 1.268021 -0.807303 -3.303072 >>> df.round(3) A B C 0 -0.939 -1.143 -0.542 1 -0.549 0.209 0.213 2 1.268 -0.807 -3.303 The DataFrame.round() method can also accept a dictionary or a Series, to specify a different precision for each column. For instance, the following examples show how to round the first column of df to one decimal place, the second to two, and the third to three decimal places: >>> # Specify column-by-column precision with a dictionary >>> df.round({"A": 1, "B": 2, "C": 3}) A B C 0 -0.9 -1.14 -0.542 1 -0.5 0.21 0.213 2 1.3 -0.81 -3.303 >>> # Specify column-by-column precision with a Series >>> decimals = pd.Series([1, 2, 3], index=["A", "B", "C"]) >>> df.round(decimals) A B C 0 -0.9 -1.14 -0.542 1 -0.5 0.21 0.213 2 1.3 -0.81 -3.303 If you need more rounding flexibility, you can apply NumPy's floor(), ceil(), and print() functions to Pandas Series and DataFrame objects: >>> np.floor(df) A B C 0 -1.0 -2.0 -1.0 1 -1.0 0.0 0.0 2 1.0 -1.0 -4.0 >>> np.ceil(df) A B C 0 -0.0 -1.0 -0.0 1 -0.0 1.0 1.0 2 2.0 -0.0 -3.0 >>> np.rint(df) A B C 0 -1.0 -1.0 -1.0 1 -1.0 0.0 0.0 2 1.0 -1.0 -3.0 The modified round_half_up() function from the previous section will also work here: >>> round_half_up(df, decimals=2) A B C 0 -0.94 -1.14 -0.54 1 -0.55 0.21 0.21 2 1.27 -0.81 -3.30Best Practices and ApplicationsNow that you have come across most of the rounding techniques, let us learn some of the best practices to make sure we round numbers in the correct way.Generate More Data and Round LaterSuppose you are dealing with a large set of data, storage can be a problem at times. For example, in an industrial oven you would want to measure the temperature every ten seconds accurate to eight decimal places, using a temperature sensor. These readings will help to avoid large fluctuations which may lead to failure of any heating element or components. We can write a Python script to compare the readings and check for large fluctuations.There will be a large number of readings as they are being recorded each and everyday. You may consider to maintain three decimal places of precision. But again, removing too much precision may result in a change in the calculation. However, if you have enough space, you can easily store the entire data at full precision. With less storage, it is always better to store at least two or three decimal places of precision which are required for calculation.In the end, once you are done computing the daily average of the temperature, you may calculate it to the maximum precision available and finally round the result.Currency Exchange and RegulationsWhenever we purchase an item from a particular place, the tax amount paid against the amount of the item depends largely on geographical factors. An item which costs you2 may cost you less (say \$1.8)  if you buy the same item from a different state. It is due to regulations set forth by the local government.In another case, when the minimum unit of currency at the accounting level in a country is smaller than the lowest unit of physical currency, Swedish rounding is done. You can find a list of such rounding methods used by various countries if you look up on the internet.If you want to design any such software for calculating currencies, keep in mind to check the local laws and regulations applicable in your present location.Reduce errorAs you are rounding numbers in a large datasets used in complex computations, your primary concern should be to limit the growth of the error due to rounding.SummaryIn this article we have seen a few methods to round numbers, out of those “rounding half to even” strategy minimizes rounding bias the best. We are lucky to have Python, NumPy, and Pandas already have built-in rounding functions to use this strategy. Here, we have learned about -Several rounding strategies, and how to implement in pure Python.Every rounding strategy inherently introduces a rounding bias, and the “rounding half to even” strategy mitigates this bias well, most of the time.You can round NumPy arrays and Pandas Series and DataFrame objects.If you enjoyed reading this article and found it to be interesting, leave a comment. To learn more about rounding numbers and other features of Python, join our Python certification course.
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How to Round Numbers in Python

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