Monday, November 1, 2021

Real Python: Python's zipapp: Build Executable Zip Applications

A Python Zip application is a quick and cool option for you to bundle and distribute an executable application in a single ready-to-run file, which will make your end users’ experience more pleasant. If you want to learn about Python applications and how to create them using zipapp from the standard library, then this tutorial is for you.

You’ll be able to create Python Zip applications as a quick and accessible way to distribute your software products to your end users and clients.

In this tutorial, you’ll learn:

  • What a Python Zip application is
  • How Zip applications work internally
  • How to build Python Zip applications with zipapp
  • What standalone Python Zip apps are and how to create them
  • How to create Python Zip apps manually using command-line tools

You’ll also learn about a few third-party libraries for creating Zip applications that overcome some limitations of zipapp.

To better understand this tutorial, you need to know how to structure Python application layouts, run Python scripts, build Python packages, work with Python virtual environments, and install and manage dependencies with pip. You also need to be comfortable using the command line or terminal.

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Getting Started With Python Zip Applications

One of the most challenging problems in the Python ecosystem is finding an effective way to distribute executable applications, such as graphical user interface (GUI) and command-line interface (CLI) programs.

Compiled programming languages, such as C, C++, and Go, can generate executable files that you can run directly on different operating systems and architectures. This ability makes it easy for you to distribute software to your end users.

However, Python doesn’t work like that. Python is an interpreted language, which means that you need a suitable Python interpreter to run your applications. There’s no direct way to generate a standalone executable file that doesn’t need an interpreter to run.

There are many solutions out there that aim to solve this issue. You’ll find tools such as PyInstaller, py2exe, py2app, Nuitka, and more. Those tools allow you to create self-contained executable applications that you can distribute to your end users. However, setting these tools up can be a complex and challenging process.

Sometimes you don’t need that extra complexity. You just need to build an executable app from a script or a small program so that you can distribute it to your end users quickly. If your application is small enough and uses pure Python code, then you can be well-served with a Python Zip application.

What Is a Python Zip Application?

PEP 441 – Improving Python ZIP Application Support formalized the idea, terminology, and specification around Python Zip applications. This type of application consists of a single file that uses the ZIP file format and contains code that Python can execute as a program. These applications rely on Python’s ability to run code from ZIP files that have a __main__.py module at their root, which works as an entry-point script.

Python has been able to run scripts from ZIP files since versions 2.6 and 3.0. The steps to achieve that are pretty straightforward. You just need a ZIP file with a __main__.py module at its root. You can then pass that file to Python, which adds it to sys.path and executes __main__.py as a program. Having the application’s archive in sys.path allows you to access its code through Python’s import system.

As a quick example of how all that works, say you’re on a Unix-like operating system, such as Linux or macOS, and you run the following commands:

$ echo 'print("Hello, World!")' > __main__.py

$ zip hello.zip __main__.py
  adding: __main__.py (stored 0%)

$ python ./hello.zip
Hello, World!

You use the echo command to create a __main__.py file containing the code print("Hello, World!"). Then you use the zip command to archive __main__.py into hello.zip. Once you’ve done that, you can run hello.zip as a program by passing the filename as an argument to the python command.

To round up the internal structure of Python Zip applications, you need a way to tell the operating system how to execute them. The ZIP file format allows you to prepend arbitrary data at the beginning of a ZIP archive. Python Zip applications take advantage of that feature to include a standard Unix shebang line in the application’s archive:

#!/usr/bin/env python3

On Unix systems, this line tells the operating system which program to use for executing the file at hand so that you can run the file directly without the python command. On Windows systems, the Python launcher properly understands the shebang line and runs the Zip application for you.

Even with a shebang line, you can always execute a Python Zip application by passing the application’s filename as an argument to the python command.

In summary, to build a Python Zip application, you need:

  • An archive that uses the standard ZIP file format and contains a __main__.py module at its root
  • An optional shebang line that specifies the appropriate Python interpreter to run the application

Read the full article at https://realpython.com/python-zipapp/ »


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