Calling Python 2 script from Python 3

Question

I have two scripts, the main is in Python 3, and the second one is written in Python 2 (it also uses a Python 2 library).

There is one method in the Python 2 script I want to call from the Python 3 script, but I don't know how to cross this bridge.

Answer 1

Calling different python versions from each other can be done very elegantly using execnet. The following function does the charm:

import execnet

def call_python_version(Version, Module, Function, ArgumentList):
    gw      = execnet.makegateway("popen//python=python%s" % Version)
    channel = gw.remote_exec("""
        from %s import %s as the_function
        channel.send(the_function(*channel.receive()))
    """ % (Module, Function))
    channel.send(ArgumentList)
    return channel.receive()

Example: A my_module.py written in Python 2.7:

def my_function(X, Y): 
    return "Hello %s %s!" % (X, Y)

Then the following function calls

result = call_python_version("2.7", "my_module", "my_function",  
                             ["Mr", "Bear"]) 
print(result) 
result = call_python_version("2.7", "my_module", "my_function",  
                             ["Mrs", "Wolf"]) 
print(result)

result in

Hello Mr Bear!
Hello Mrs Wolf!

What happened is that a 'gateway' was instantiated waiting for an argument list with channel.receive(). Once it came in, it as been translated and passed to my_function. my_function returned the string it generated and channel.send(...) sent the string back. On other side of the gateway channel.receive() catches that result and returns it to the caller. The caller finally prints the string as produced by my_function in the python 3 module.