[Python-Dev] PEP 414 - Unicode Literals for Python 3

[Michael Foord]

On 26 Feb 2012, at 17:45, Antoine Pitrou wrote:

> 
> Hi,
> 
> On Sat, 25 Feb 2012 20:23:39 +0000
> Armin Ronacher <armin.ronacher at active-4.com> wrote:
>> 
>> I just uploaded PEP 414 which proposes am optional 'u' prefix for string
>> literals for Python 3.
>> 
>> You can read the PEP online: http://www.python.org/dev/peps/pep-0414/
> 
> I don't understand this sentence:
> 
>> The automatic upgrading of binary strings to unicode strings that
>> would be enabled by this proposal would make it much easier to port
>> such libraries over.
> 
> What "automatic upgrading" is that talking about?

If you use native string syntax (no prefix) then moving from Python 2 to Python 3 automatically "upgrades" (I agree an odd choice of word) byte string literals to unicode string literals.

> 
>> For instance, the urllib module in Python 2 is using byte strings,
>> and the one in Python 3 is using unicode strings.
> 
> Are you talking about urllib.parse perhaps?
> 
>> By leveraging a native string, users can avoid having to adjust for
>> that.
> 
> What does "leveraging a native string" mean here?

By using native string syntax (without the unicode literals future import) then apis that take a binary string in Python 2 and a unicode string in Python 3 "just work" with the same syntax. You are "leveraging" native syntax to use the same apis with different types across the different version of Python. 


> 
>> The following is an incomplete list of APIs and general concepts that
>> use native strings and need implicit upgrading to unicode in Python
>> 3, and which would directly benefit from this support
> 
> I'm confused. This PEP talks about unicode literals, not native string
> literals, so why would these APIs "directly benefit from this support"?

Because sometimes in your code you want to specify "native strings" and sometimes you want to specify Unicode strings. There is no single *syntax* that is compatible with both Python 2 and Python 3 that permits this. (If you use "u" for Unicode in Python 2 and no prefix for native strings then your code is Python 3 incompatible, if you use the future import so that your strings are unicode in both Python 2 and Python 3 then you lose the syntax for native strings.)

Michael


> 
> Thanks
> 
> Antoine.
> 
> 
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