One option is to specify the specific version of the Python interpreter using the hash bang:
#! /usr/bin/env python2.6
Another option is to check sys.version_info, for example:
if (sys.version_info[0] != 2) or (sys.version_info[1]<6):
if sys.version_info[0] > 2:
print("Version 2.6+, and not 3.0+ needed.")
sys.exit(1)
else:
print "Version 2.6+, needed. Please upgrade Python."
sys.exit(1)
The hash bang is probably the best option, as it actually ensures that the script will be interpreted by "python2.6" instead of some other interpreter; however, there are some disadvantages:
- This will only work on UNIX-like systems that use the hash bang.
- This will won't work if Python2.7 is installed, but not Python 2.6.
As a workaround, what you can do is create a "launcher" Python script that checks for "python2.6"... "python2.9", which is the last possible version of the 2.6+ line before Python 3.0+. This launcher script can then invoke your main program using whichever python interpreter it finds in the search process. You will have to make your launcher script in a way that uses elements common to most Python versions.
Borrowing from test if executable exists in Python:
def which(program):
import os
def is_exe(fpath):
return os.path.exists(fpath) and os.access(fpath, os.X_OK)
fpath, fname = os.path.split(program)
if fpath:
if is_exe(program):
return program
else:
for path in os.environ["PATH"].split(os.pathsep):
exe_file = os.path.join(path, program)
if is_exe(exe_file):
return exe_file
return None
def first_which(progs):
for prog in progs:
progloc = which(prog)
if progloc != None:
return progloc
return None
def main():
interpreter=first_which(["python2.6","python2.7","python2.8","python2.9"])
# Invoke your program using "interpreter"
# You will need to use os.popen or subprocess,
# depending on the version of Python which which
# this launcher script was invoked...
My own opinion is that the method above is more complicated than necessary, and I would just go with the hash bang... or I would write out the hash bang to the Python file at deployment time, using a language other than Python (for which the version wouldn't be an issue... otherwise, it becomes a recursive problem).
I would also strongly urge you NOT to include a copy of Python in your software distribution. This will make your download much larger, and it will annoy users who already have a valid installation of Python available. Instead, you should simply direct users to download and install the appropriate version if it isn't available.
