Differences In The Ways To Running Python Scripts

I have a very simple Python question, with examples using Django. When running a Python script, do I always have to precede the script filename with the python command? In the Dja

Solution 1:

The answer lies in a combination of two things:

1. The shebang, the first line of a file.
2. The permissions on the file, namely whether the executable flag is set or not.

Consider the first line of django-manage.py. On my system it is at /usr/local/bin/django-admin.py and the first line is:

#!/usr/bin/python2.7

And the permissions on the file:

-rwxr-xr-x 1 root root 127 Jan  9 13:38 /usr/local/bin/django-admin.py

The shebang tells my OS that I want to execute the file with the interpreter at /usr/bin/python2.7. The x characters in the permissions say that it is an executable file. I don't need to specify python beforehand, because the OS can figure out that stuff automatically from the above pieces of information.

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Now for a freshly created manage.py, which I made by running django-admin.py startproject mysite, it looks like this:

#!/usr/bin/env python

And the permissions:

-rw-r--r--1 wim wim 249 Feb 1717:33 manage.py

The shebang indicates to use whatever python interpreter my env is pointing at, so that part is in place already. But the file lacks executable permissions, so just running ./manage.py won't work (yet).

I can make it behave the same as django-manage.py by explicitly setting the executable flag using chmod +x manage.py. After that, you should see the x flags set when you do ls -l in the directory, and you should be able to run the file without specifying python beforehand.

Note: you do still have to use ./manage.py not just manage.py, this discrepancy is because django-admin.py lives in /usr/local/bin/ which is contained in PATH whereas the manage.py file likely doesn't. So we explicitly specify the path at the shell, where . refers to the current directory.

Solution 2:

You can make the script executable by using chmod +x script.py, but you need the shebang line, usually #!/usr/bin/python If you are using a script heavily on a unix-based maching (mac,linux) making an alias can be useful: alias command="python path/to/script.py"