Alternative to contextlib.nested with variable number of context managers

Question

We have code that invokes a variable number of context managers depending on runtime parameters:

from contextlib import nested, contextmanager

@contextmanag         


        

Answer 1

import sys
import contextlib

class nodeA(object):

    def __init__(self):
        print( '__init__ nodeA')

    def __enter__(self):
        print( '__enter__ nodeA')

    def __exit__(self, a, b, c):
        print( '__exit__ nodeA')

class nodeB(object):

    def __init__(self):
        print( '__init__ nodeB')

    def __enter__(self):
        print( '__enter__ nodeB')

    def __exit__(self, a, b, c):
        print( '__exit__ nodeB')

class nodeC(object):

    def __init__(self):
        print( '__init__ nodeC')

    def __enter__(self):
        print( '__enter__ nodeC')

    def __exit__(self, a, b, c):
        print( '__exit__ nodeC')

print( 'Start...')

a = nodeA()
b = nodeB()
c = nodeC()

print( 'Python version: %s' % (sys.version))

if sys.version.startswith('2'):
    print('Use python 2!')
    with contextlib.nested(a, b, c):
        print('hallo?')

if sys.version.startswith('3'):
    print('Use python 3!')
    with contextlib.ExitStack() as stack:
        [stack.enter_context(arg) for arg in [a,b,c]]

print('...end!')