[PATCH] py3: have an utility function to return string

[Pulkit Goyal]

On Thu, Sep 15, 2016 at 7:06 PM, Yuya Nishihara <yuya at tcha.org> wrote:
> On Wed, 14 Sep 2016 22:45:27 +0530, Pulkit Goyal wrote:
>> # HG changeset patch
>> # User Pulkit Goyal <7895pulkit at gmail.com>
>> # Date 1473787789 -19800
>> #      Tue Sep 13 22:59:49 2016 +0530
>> # Node ID ec133d50af780e84a6a24825b52d433c10f9cd55
>> # Parent  85bd31515225e7fdf9bd88edde054db2c74a33f8
>> py3: have an utility function to return string
>>
>> There are cases when we need strings and can't use bytes in python 3.
>> We need an utility function for these cases. I agree that this may not
>> be the best possible way out. I will be happy if anybody else can suggest
>> a better approach. We need this functions for os.path.join(),
>
> We should stick to bytes for filesystem API, and translate bytes to unicode
> at VFS layer as necessary.
>
> https://www.mercurial-scm.org/wiki/WindowsUTF8Plan
>
> (Also, we'll have to disable PEP 528 and 529 on Python 3.6, which will break
> existing repositories.)
>
> https://docs.python.org/3.6/whatsnew/3.6.html
>
>> __slots__
>
> __slots__ can be considered private data, so just use u''.
>
>> and few more things.
>
> for instance?
This function was motivated from Gregory's reply to
https://www.mercurial-scm.org/pipermail/mercurial-devel/2016-August/086704.html
, unfortunately I see that he replied to me only so I pasted it here
https://bpaste.net/show/ab0d3ea39749

I am going through python documentation and there are things like
__slots__, is_frozen() which accepts str in both py2 and py3. Since
they are not same, I made this function to get help in such cases. If
we can use unicodes in __slots__ in py2, than thats good.
>
>> +# This function converts its arguments to strings
>> +# on the basis of python version. Strings in python 3
>> +# are unicodes and our transformer converts everything to bytes
>> +# in python 3. So we need to decode it to unicodes in
>> +# py3.
>> +
>> +def coverttostr(word):
>> +    if sys.version_info[0] < 3:
>> +        assert isinstance(word, str), "Not a string in Python 2"
>> +        return word
>> +    # Checking word is bytes because we have the transformer, else
>> +    # raising error
>> +    assert isinstance(word, bytes), "Should be bytes because of transformer"
>> +    return word.decode(sys.getfilesystemencoding())
>
> Can we assume 'word' was encoded in file-system codec?

Yeah because of the tranformer, we added b'' everywhere.