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from contextlib import contextmanager
import sys
from io import StringIO
@contextmanager
def captured_output(stream_name):
"""Return a context manager used by captured_stdout/stdin/stderr
that temporarily replaces the sys stream *stream_name* with a StringIO.
This function and the following ``captured_std*`` are copied
from CPython's ``test.support`` module.
"""
orig_stdout = getattr(sys, stream_name)
setattr(sys, stream_name, StringIO())
try:
yield getattr(sys, stream_name)
finally:
setattr(sys, stream_name, orig_stdout)
def captured_stderr():
"""Capture the output of sys.stderr:
with captured_stderr() as stderr:
print('hello', file=sys.stderr)
self.assertEqual(stderr.getvalue(), 'hello\n')
"""
return captured_output('stderr')
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