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To: python-list@python.org
From: Mark Lawrence <breamoreboy@yahoo.co.uk>
Subject: Re: io.open vs. codecs.open
Date: Wed, 04 Mar 2015 20:15:59 +0000
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On 04/03/2015 19:56, Steven D'Aprano wrote:
> Albert-Jan Roskam wrote:
>
>> Hi,
>>
>> Is there a (use case) difference between codecs.open and io.open? What is
>> the difference? A small difference that I just discovered is that
>> codecs.open(somefile).read() returns a bytestring if no encoding is
>> specified*), but a unicode string if an encoding is specified. io.open
>> always returns a unicode string.
>
> What version of Python are you using?
>
> In Python 3, io.open is used as the built-in open. I believe this is
> guaranteed, and not just an implementation detail.
>
> The signatures and capabilities are quite different:
>
> codecs.open:
>
> open(filename, mode='rb', encoding=None, errors='strict', buffering=1)
>
> io.open:
>
> open(file, mode='r', buffering=-1, encoding=None,
>           errors=None, newline=None, closefd=True, opener=None)
>
> io.open does *not* always produce Unicode strings. If you pass 'rb' as the
> mode, the file is opened in binary mode, not text mode, and the read()
> method will return bytes.
>
> As usual, help() in the interactive interpreter is your friend.
> help(codecs.open) and help(io.open) will explain the many differences
> between them, including that codecs.open always opens the file in binary
> mode.
>
> As for use-cases, I think that codecs.open is mostly a left-over from the
> Python 2 days when the built-in open had a much simpler interface and fewer
> capabilities. In Python 2, built-in open doesn't take an encoding argument,
> so if you want to use something other than binary mode or the default
> encoding, you were supposed to use codecs.open.
>
> In Python 2.6, the io module was added to Python 2 to aid in porting to
> Python 3. The docs say:
>
>      New in version 2.6.
>
>      The io module provides the Python interfaces to stream handling.
>      Under Python 2.x, this is proposed as an alternative to the
>      built-in file object, but in Python 3.x it is the default
>      interface to access files and streams.
>
> https://docs.python.org/2/library/io.html
>
>
> To summarise:
>
> * In Python 2, if you want to supply an encoding to open, use codecs.open
> (before 2.6) or io.open (2.6 and later);
>
> * If you want the enhanced capabilities of Python 3 open, use io.open;
>
> * In Python 3, io.open is the same thing as built-in open;
>
> * And codecs.open is (I think) mostly there for backwards compatibility.
>

See http://bugs.python.org/issue8796 "Deprecate codecs.open()".

-- 
My fellow Pythonistas, ask not what our language can do for you, ask
what you can do for our language.

Mark Lawrence