gistfile1.py

$ python3 wtf.py 
foo
bar
b''

wtf.py

import io
import sys
import contextlib


class _NonClosingTextIOWrapper(io.TextIOWrapper):
    def __del__(self):
        pass


@contextlib.contextmanager
def capture_stdout(and_stderr=False):
    ll_stream = io.BytesIO()
    stream = _NonClosingTextIOWrapper(ll_stream, sys.stdout.encoding,
                                      sys.stdout.errors)
    old_stdout = sys.stdout
    sys.stdout = stream

    if and_stderr:
        old_stderr = sys.stderr
        sys.stderr = stream

    try:
        yield ll_stream
    finally:
        stream.flush()
        sys.stdout = old_stdout
        sys.stdout.buffer.write(ll_stream.getvalue())
        if and_stderr:
            sys.stderr = old_stderr


with capture_stdout() as out:
    print('foo')
    print('bar')
    x = out.getvalue()

print(repr(x))