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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def call(exe, *argv):
 """ Run a command, returning its output, or None if it fails. """

    exes = which(exe)
    if not exes:
        returnValue(None)
    stdout, stderr, value = yield getProcessOutputAndValue(
        exes[0], argv, env=os.environ.copy()
    )
    if value:
        returnValue(None)
    returnValue(stdout.decode('utf-8').rstrip('\n'))