[Python-Dev] Make re.compile faster

[Barry Warsaw]

On Oct 3, 2017, at 01:35, Serhiy Storchaka <storchaka at gmail.com> wrote:
> 
>> diff --git a/Lib/string.py b/Lib/string.py
>> index b46e60c38f..fedd92246d 100644
>> --- a/Lib/string.py
>> +++ b/Lib/string.py
>> @@ -81,7 +81,7 @@ class Template(metaclass=_TemplateMetaclass):
>>      delimiter = '$'
>>      idpattern = r'[_a-z][_a-z0-9]*'
>>      braceidpattern = None
>> -    flags = _re.IGNORECASE
>> +    flags = _re.IGNORECASE | _re.ASCII
>>      def __init__(self, template):
>>          self.template = template
>> patched:
>> import time:      1191 |       8479 | string
>> Of course, this patch is not backward compatible. [a-z] doesn't match with 'ı' or 'ſ' anymore.
>> But who cares?
> 
> This looks like a bug fix. I'm wondering if it is worth to backport it to 3.6. But the change itself can break a user code that changes idpattern without touching flags. There is other way, but it should be discussed on the bug tracker.

It’s definitely an API change, as I mention in the bug tracker.  It’s *probably* safe in practice given that the documentation does say that identifiers are ASCII by default, but it also means that a client who wants to use Unicode previously didn’t have to touch flags, and after this change would now have to do so.  `flags` is part of the public API.

Maybe for subclasses you could say that if delimiter, idpattern, or braceidpattern are anything but the defaults, fall back to just re.IGNORECASE.

Cheers,
-Barry

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