Where does the shebang in tool-launching Python scripts come from?

Question

Several widely used Python tools — such as pip , yolk and ipython — are launched by scripts with a shebang specifying what Python instance should be used to run them. How is the contents of this line determined?

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For example, on OS X machine, where I have been using Apple's Python, this line reads

#!/usr/bin/python

What would happen if I installed the python.org version, which is placed in

/Library/Frameworks/Python.framework/Versions/2.7/python 

with a symlink at

/usr/local/bin/python

and then updated or re-installed a tool? If I updated a tool would the line change? Would I have to fully reinstall (rather than simply updating) each tool to force a change? What would the line change to? Would it be

#!/usr/local/bin

or

#!/Library/Frameworks/Python.framework/Versions/2.7

Is there a way to make it

#!/usr/bin/env python

Answer 1

The line comes from the sys.executable value .

If you symlink the python executable, and run Python from that symlink, sys.executable would use the new path. Updating or reinstalling the tool would reflect the changed executable path, yes.

I am not aware of any method to make pip and friends use #!/usr/bin/env python instead. That'd be a bad idea, really, as that would make it harder to use the correct Python all the time, the one where the installed packages can be found needed to run the command-line script.