CODEWITHSUNDEEP
pythonpython-2.7python-3.x
Mikko Ohtamaa
Mikko Ohtamaa

Reputation: 83758

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

I have a Python codebase, built for Python 3, which uses Python 3 style open() with encoding parameter:

https://github.com/miohtama/vvv/blob/master/vvv/textlineplugin.py#L47

    with open(fname, "rt", encoding="utf-8") as f:

Now I'd like to backport this code to Python 2.x, so that I would have a codebase which works with Python 2 and Python 3.

What's the recommended strategy to work around open() differences and lack of encoding parameter?

Could I have a Python 3 open() style file handler which streams bytestrings, so it would act like Python 2 open()?

Upvotes: 189

Views: 406157

Answers (6)

Flimm
Flimm

Reputation: 150483

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"))

Upvotes: 32

MarkH
MarkH

Reputation: 469

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

Upvotes: 1

Lennart Regebro
Lennart Regebro

Reputation: 172179

1. To get an encoding parameter in Python 2:

If you only need to support Python 2.6 and 2.7 you can use io.open instead of open. io is the new io subsystem for Python 3, and it exists in Python 2,6 ans 2.7 as well. Please be aware that in Python 2.6 (as well as 3.0) it's implemented purely in python and very slow, so if you need speed in reading files, it's not a good option.

If you need speed, and you need to support Python 2.6 or earlier, you can use codecs.open instead. It also has an encoding parameter, and is quite similar to io.open except it handles line-endings differently.

2. To get a Python 3 open() style file handler which streams bytestrings:

open(filename, 'rb')

Note the 'b', meaning 'binary'.

Upvotes: 191

YaOzI
YaOzI

Reputation: 17458

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.

Upvotes: 2

TylerTemp
TylerTemp

Reputation: 1042

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

Upvotes: 9

mfussenegger
mfussenegger

Reputation: 3971

I think 

from io import open

should do.

Upvotes: 74

Related Questions