I have a Python codebase, built for Python 3, which uses Python 3 style open() with encoding parameter:
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
from io import open
If you only need to support Python 2.6 and 2.7 you can use
io.open instead of
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.
open()style file handler which streams bytestrings:
Note the ‘b’, meaning ‘binary’.
This may do the trick:
import sys if sys.version_info > 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
opener do not work
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"))
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
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