How to Create a Shebang for Both Python 2 and Python 3 Compatible Scripts

Learn how to construct a shebang in your Python script that works seamlessly with both Python 2 and Python 3, ensuring compatibility across different systems.
---
This video is based on the question https://stackoverflow.com/q/69759506/ asked by the user 'Bri Bri' ( https://stackoverflow.com/u/1079430/ ) and on the answer https://stackoverflow.com/a/69760814/ provided by the user 'that other guy' ( https://stackoverflow.com/u/1899640/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Is it possible to construct a shebang that works for both Python 2 and 3?

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
How to Create a Shebang for Both Python 2 and Python 3 Compatible Scripts

Creating a Python script that runs smoothly on both Python 2 and Python 3 can be quite challenging, especially when it comes to setting up the correct shebang. A shebang is the first line of a script that indicates which interpreter should be used to run the file. The problem arises when the script needs to be executed on systems that may only have one version of Python installed.

The Challenge: Compatibility Across Python Versions

For many developers, the need to write a single script that can function with both Python versions is a common requirement. Traditionally, specific shebangs are used for each version:

For Python 2:

[[See Video to Reveal this Text or Code Snippet]]

For Python 3:

[[See Video to Reveal this Text or Code Snippet]]

The issue lies in the fact that if a system only has Python 3 installed, using the Python 2 shebang will lead to failure, as systems generally do not symlink python to python3. This situation can be especially urgent since some operating systems, like macOS, are starting to move away from Python 2 entirely.

The Solution: A Flexible Shebang Approach

While the straightforward solution is to simply require python3, which ensures that the script will run under that interpreter, there is an alternative method to make your script work under any installation of Python.

Using a Shell Wrapper

You can embed a shell script wrapper directly in your Python file that checks for the first available Python interpreter. Here’s how:

[[See Video to Reveal this Text or Code Snippet]]

Breakdown of the Shebang Code

!/bin/sh: This specifies that the file will be executed as a shell script.

''': ': This is a common idiom to prevent the shell from executing the next part immediately. It serves as a placeholder for a multi-line shell command.

for name in python3 python2 python: This loop checks for the availability of each Python interpreter.

type "$name" /dev/null 2 &1: This tests if the current $name (either python3, python2, or python) is available on the system.

exec "$name" "$0" "$@ ": If one of the interpreters is found, it executes the script using that interpreter.

echo &2 "Please install python": If none of the interpreters are available, it outputs an error message to stderr.

exit 1: This exits with a status code indicating an error.

Pros and Cons of This Method

Pros:

Flexibility: Works with either Python version as long as one is installed.

Ease of Use: You can distribute one script for various environments without worrying about Python version discrepancies.

Cons:

Complexity: This method may be less transparent than directly requiring a specific Python version.

Overhead: Slightly more processing occurs at the script startup due to the interpreter check.

Conclusion

By utilizing a shell script wrapper, you can effectively create a shebang that accommodates both Python 2 and Python 3 in a single script. While it’s often simpler to use just Python 3 and make it a prerequisite, this method provides a robust solution for environments where you might encounter differing Python installations.

Now that you have this essential information, you can improve your Python development practices and ensure greater script compatibility. Happy coding!