#!/usr/bin/env python
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# import the print function which is used in python 3.x
from __future__ import print_function

import itertools
import subprocess
import os

# http://stackoverflow.com/questions/1214496/how-to-get-environment-from-a-subprocess-in-python
#def validate_pair(ob):
#    try:
#        if not (len(ob) == 2):
#            print("Unexpected result:", ob, file = sys.stderr)
#            raise ValueError
#    except:
#        return False
#    return True

def consume(iterator):
    try:
        while True:
            next(iterator)
    except StopIteration:
        pass

def get(env_cmd, initial = None, arguments = None):
    """
    Take a command (either a single command or list of arguments)
    and return the environment created after running that command.
    Note that if the command must be a batch file or .cmd file, or the
    changes to the environment will not be captured.

    If initial is supplied, it is used as the initial environment passed
    to the child process.
    """
    if not os.path.lexists(env_cmd):
        raise Exception("Can not find {0} to get an environment from it.".format(env_cmd))

    #if not isinstance(env_cmd, (list, tuple)):
    #    env_cmd = [env_cmd]
    # construct the command that will alter the environment
    #env_cmd = subprocess.list2cmdline(env_cmd)

    # create a tag so we can tell in the output when the proc is done
    tag = 'Done running command'
    # construct a cmd.exe command to do accomplish this
    cmd = 'cmd.exe /s /c "\"{env_cmd}\" {arguments}&& echo "{tag}" && set"'.format(**vars())

    # launch the process
    proc = subprocess.Popen(cmd, stdout = subprocess.PIPE, env = initial)
    # parse the output sent to stdout
    lines = proc.stdout
    # consume whatever output occurs until the tag is reached
    consume(itertools.takewhile(lambda line: tag not in line, lines))
    # parse key/values into pairs
    pairs = (line.rstrip().split('=', 1) for line in lines)
    # make sure the pairs are valid
    valid_pairs = (pair for pair in pairs if len(pair) == 2)
    # construct a dictionary of the pairs
    result = dict(valid_pairs)
    # let the process finish
    proc.communicate()
    return result