If am am writing stdout and stderr to a file

Question

If am am writing stdout and stderr to a file

is there a way I can capture that in the code and assign it to a variable?

upgradeproc = subprocess.Popen(upgradecmd, shell=True, stdout=stdout_handle, stderr=stderr_handle, preexec_fn=self.demote())

stdout,stderr = upgradeproc.communicate() # Always returns NONE

https://docs.python.org/2.7/library/subprocess.html#subprocess.Popen.communicate