Bash – Correct handling of Python2 and Python3

bashpathpythonunix-philosophy

What is the correct way running scripts that depend on python2.x but on a system where python3.x is aliased with python.

The solution should take into account the following things :

Python2 should be used only for that bash run
every script that is run form subsequently should also use Python2
The change should be temporary

One solution is temporary making alias and setting the location for Python2 at the beginning of the full PATH.

What is the right (*nix) way to handle this ?

Best Answer

The correct way is to use #!/usr/bin/python2 as shbang line. More and more distributions support this now, and even upstream python development has adopted it.

Related Solutions

Python == python2 OR python == python3 ? How to package, distribute python py2k scripts

A script can check its Python version and, if that's Python 3, re-start itself using Python 2. Add the following near the head of the script:

if sys.version > '3':
  python2 = os.popen('which python2 2> /dev/null').read().rstrip()
  if python2:
    args = sys.argv[:]
    args.insert(0,python2)
    os.execv(python2,args)
  else:
    sys.exit("%s requires Python Version 2 (python2 not in PATH)" % os.path.basename(__file__))

This uses the system's which command to locate python2 in the environment's PATH. It then relaunches itself with that (or aborts if unable to find it).

Note that the script does need to be valid Python 3 syntax for it to start in Python 3.

Also, any output should be flushed before the execv call or it will be lost. Adding, for example, sys.stdout.flush() just before the call to execv will flush any print statements.

Linux – python2 and OpenSSL don’t play together on Kali – how to fix

I'm assuming you have installed pip from the distribution repositories?

If so, just remove current version of pip and install it with get-pip.py:

curl -o ./get-pip.py https://bootstrap.pypa.io/get-pip.py
python3 ./get-pip.py
python2 ./get-pip.py

This should pull all the appropriate dependencies and your pip will start working again.

Best Answer

Related Solutions

Python == python2 OR python == python3 ? How to package, distribute python py2k scripts

Linux – python2 and OpenSSL don’t play together on Kali – how to fix

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