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After the stdout stream has been overwritten and detached, the method shutils.get_terminal_size throws a ValueError exception and no fallback value is returned.
Code to reproduce it:
 >>> import os, sys, codecs, shutils
 >>> sys.stdout = codecs.getwriter("utf-8")(sys.stdout.detach())
 >>> os.get_terminal_size()
 os.terminal_size(columns=160, lines=37)
 >>> shutil.get_terminal_size((200, 30))
 Traceback (most recent call last):
 File "<stdin>", line 1, in <module> 
 File "/usr/lib64/python3.4/shutil.py", line 1057, in get_terminal_size
 size = os.get_terminal_size(sys.__stdout__.fileno())
 ValueError: underlying buffer has been detached
Is this the expected behavior ? IMHO, the given fallback values should be returned.
The official doc: "If the terminal size cannot be successfully queried, either because the system doesn’t support querying, or because we are not connected to a terminal, the value given in fallback parameter is used. fallback defaults to (80, 24) which is the default size used by many terminal emulators"
BTW, the function os.get_terminal_size() returns the correct size when it's invoked without parameters, maybe It could be a good fallback if sys.__stdout__ is not available and there isn't any user fallback values.