Backporting Python 3 open(encoding="utf-8") to Python 2

I think

from io import open

should do.

Here's one way:

with open("filename.txt", "rb") as f:
    contents = f.read().decode("UTF-8")

Here's how to do the same thing when writing:

with open("filename.txt", "wb") as f:
    f.write(contents.encode("UTF-8"))

This may do the trick:

import sys
if sys.version_info[0] > 2:
    # py3k
    pass
else:
    # py2
    import codecs
    import warnings
    def open(file, mode='r', buffering=-1, encoding=None,
             errors=None, newline=None, closefd=True, opener=None):
        if newline is not None:
            warnings.warn('newline is not supported in py2')
        if not closefd:
            warnings.warn('closefd is not supported in py2')
        if opener is not None:
            warnings.warn('opener is not supported in py2')
        return codecs.open(filename=file, mode=mode, encoding=encoding,
                    errors=errors, buffering=buffering)

Then you can keep you code in the python3 way.

Note that some APIs like newline, closefd, opener do not work

If you are using six, you can try this, by which utilizing the latest Python 3 API and can run in both Python 2/3:

import six

if six.PY2:
    # FileNotFoundError is only available since Python 3.3
    FileNotFoundError = IOError
    from io import open

fname = 'index.rst'
try:
    with open(fname, "rt", encoding="utf-8") as f:
        pass
        # do_something_with_f ...
except FileNotFoundError:
    print('Oops.')

And, Python 2 support abandon is just deleting everything related to six.

Not a general answer, but may be useful for the specific case where you are happy with the default python 2 encoding, but want to specify utf-8 for python 3:

if sys.version_info.major > 2:
    do_open = lambda filename: open(filename, encoding='utf-8')
else:
    do_open = lambda filename: open(filename)

with do_open(filename) as file:
    pass