Decorator to avoid UnicodeEncodeError in Python 3 print ()

I wrote it after practicing the decorator. It has been confirmed to work with Python 3.3.0.

Since it is a mundane content, I will omit the explanation, but by default, it is

• If the encoding of standard input / output + error output is'ascii', change it to'utf-8'.
• Changed errors in standard I / O + error output to'backslashreplace'

It is designed to do.

There seems to be room for reconsideration about the specifications, so if you have any good ideas, please let us know in the comments. We also welcome any bugs or bad points.

fixprint.py

#!/usr/bin/env python3
# vim:fileencoding=utf-8

# Copyright (c) 2013 Masami HIRATA <[email protected]>
# All rights reserved.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions are met:
#
#     1. Redistributions of source code must retain the above copyright notice,
#        this list of conditions and the following disclaimer.
#
#     2. Redistributions in binary form must reproduce the above copyright
#        notice, this list of conditions and the following disclaimer in the
#        documentation and/or other materials provided with the distribution.
#
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
# AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
# ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
# LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
# CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
# SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
# INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
# CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
# ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
# POSSIBILITY OF SUCH DAMAGE.

__all__ = ["fixprint"]

import codecs
from collections import namedtuple
from functools import partial, wraps
import sys

STREAMS = ("stdin", "stdout", "stderr")
ARGUMENTS = ("encoding", "errors")
ENCODING_DEFAULT = 'utf-8'
ERRORS_DEFAULT = 'backslashreplace'
ENCODING_ASCII = 'ascii'
ENCODING_UTF8 = 'utf-8'
ANY = None


def fixprint(function=None, encoding=None, *, errors=None):
    """This decorator changes the 'encoding' and 'errors' of stdin/out/err

        >>> import sys
        >>> @fixprint(encoding='latin-1', errors='replace')
        ... def spam():
        ...     print("sys.stdout.encoding in spam() is '{}'".format(
        ...           sys.stdout.encoding))
        ...
        >>> @fixprint('utf-8')
        ... def ham():
        ...     spam()
        ...     print("sys.stdout.encoding in ham() is '{}'".format(
        ...           sys.stdout.encoding))
        ...
        >>> ham()  # doctest: +SKIP
        sys.stdout.encoding in spam() is 'latin-1'
        sys.stdout.encoding in ham() is 'utf-8'
        >>>
    """

    if not callable(function):
        if function is not None:
            if encoding is not None:
                # @fixprint("utf-8", encoding="ascii")  # WRONG
                raise TypeError("fixprint() takes 1 positional argument " +
                                "but 2 were given")
            else:
                # @fixprint("utf-8")  # CORRECT
                encoding = function
        return partial(fixprint, encoding=encoding, errors=errors)

    def _setarg(base, stream, argument, value):
        if stream is ANY:
            streams = STREAMS
        else:
            streams = (stream,)

        if argument is ANY:
            arguments = ARGUMENTS
        else:
            arguments = (argument,)

        for a_stream in streams:
            if type(getattr(base, a_stream)) is property:
                setattr(base, a_stream, namedtuple("_Stream", ARGUMENTS))

            for an_argument in arguments:
                setattr(getattr(base, a_stream), an_argument, value)

    def _reopen_stream(old_stream, new_stream):
        old_stream.flush()
        return open(old_stream.fileno(),
                    old_stream.mode,
                    encoding=new_stream.encoding,
                    errors=new_stream.errors,
                    closefd=False)

    @wraps(function)
    def _fixprint(*args, **kwargs):
        saved = namedtuple("_Saved", STREAMS)
        fixed = namedtuple("_Fixed", STREAMS)
        for stream in STREAMS:
            for argument in ARGUMENTS:
                value = getattr(getattr(sys, stream), argument)
                _setarg(saved, stream, argument, value)
                _setarg(fixed, stream, argument, value)

        normalize = lambda encoding: codecs.lookup(encoding).name

        if encoding is not None:
            _setarg(fixed, ANY, "encoding", encoding)
        elif normalize(saved.stdout.encoding) == normalize(ENCODING_ASCII):
            fixed.stdin.encoding = ENCODING_DEFAULT
            fixed.stdout.encoding = fixed.stderr.encoding = ENCODING_DEFAULT

        if errors is not None:
            _setarg(fixed, ANY, "errors", errors)
        elif normalize(fixed.stdout.encoding) != normalize(ENCODING_UTF8):
            _setarg(fixed, ANY, "errors", ERRORS_DEFAULT)

        sys.stdin = _reopen_stream(sys.stdin, fixed.stdin)
        sys.stdout = _reopen_stream(sys.stdout, fixed.stdout)
        sys.stderr = _reopen_stream(sys.stderr, fixed.stderr)

        try:
            result = function(*args, **kwargs)
        finally:
            sys.stdin = _reopen_stream(sys.stdin, saved.stdin)
            sys.stdout = _reopen_stream(sys.stdout, saved.stdout)
            sys.stderr = _reopen_stream(sys.stderr, saved.stderr)

        return result

    return _fixprint