Should I put #! (shebang) in Python scripts, and what form should it take?
Should I put the shebang in my Python scripts? In what form?
#!/usr/bin/env python
or
#!/usr/local/bin/python
Are these equally portable? Which form is used most?
Note: the tornado project uses the shebang. On the other hand the Django project doesn't.
The shebang line in any script determines the script's ability to be executed like a standalone executable without typing python beforehand in the terminal or when double clicking it in a file manager (when configured properly). It isn't necessary but generally put there so when someone sees the file opened in an editor, they immediately know what they're looking at. However, which shebang line you use IS important.
Correct usage for Python 3 scripts is:
#!/usr/bin/env python3
This defaults to version 3.latest. For Python 2.7.latest use python2 in place of python3 .
The following should NOT be used (except for the rare case that you are writing code which is compatible with both Python 2.x and 3.x):
#!/usr/bin/env python
The reason for these recommendations, given in PEP 394, is that python can refer either to python2 or python3 on different systems. It currently refers to python2 on most distributions, but that is likely to change at some point.
Also, DO NOT Use:
#!/usr/local/bin/python
"python may be installed at /usr/bin/python or /bin/python in those cases, the above #! will fail."
--"#!/usr/bin/env python" vs "#!/usr/local/bin/python"
It's really just a matter of taste. Adding the shebang means people can invoke the script directly if they want (assuming it's marked as executable); omitting it just means python has to be invoked manually.
The end result of running the program isn't affected either way; it's just options of the means.
Should I put the shebang in my Python scripts?
Put a shebang into a Python script to indicate:
python executable explicitly Are these equally portable? Which form is used most?
If you write a shebang manually then always use #!/usr/bin/env python unless you have a specific reason not to use it. This form is understood even on Windows (Python launcher).
Note: installed scripts should use a specific python executable eg, /usr/bin/python or /home/me/.virtualenvs/project/bin/python . It is bad if some tool breaks if you activate a virtualenv in your shell. Luckily, the correct shebang is created automatically in most cases by setuptools or your distribution package tools (on Windows, setuptools can generate wrapper .exe scripts automatically).
In other words, if the script is in a source checkout then you will probably see #!/usr/bin/env python . If it is installed then the shebang is a path to a specific python executable such as #!/usr/local/bin/python (NOTE: you should not write the paths from the latter category manually).
To choose whether you should use python , python2 , or python3 in the shebang, see PEP 394 - The "python" Command on Unix-Like Systems:
... python should be used in the shebang line only for scripts that are source compatible with both Python 2 and 3.
in preparation for an eventual change in the default version of Python, Python 2 only scripts should either be updated to be source compatible with Python 3 or else to use python2 in the shebang line.