[Python-ideas] Adding str.isascii() ?

[M.-A. Lemburg]

On 26.01.2018 09:53, Chris Angelico wrote:
> On Fri, Jan 26, 2018 at 7:42 PM, INADA Naoki <songofacandy at gmail.com> wrote:
>> Hi.
>>
>> Currently, int(), str.isdigit(), str.isalnum(), etc... accepts
>> non-ASCII strings.
>>
>>>>> s =  １２３"
>>>>> s
>> '１２３'
>>>>> s.isdigit()
>> True
>>>>> print(ascii(s))
>> '\uff11\uff12\uff13'
>>>>> int(s)
>> 123
>>
>> But sometimes, we want to accept only ascii string.  For example,
>> ipaddress module uses:
>>
>> _DECIMAL_DIGITS = frozenset('0123456789')
>> ...
>> if _DECIMAL_DIGITS.issuperset(str):
>>
>> ref: https://github.com/python/cpython/blob/e76daebc0c8afa3981a4c5a8b54537f756e805de/Lib/ipaddress.py#L491-L494
>>
>> If str has str.isascii() method, it can be simpler:
>>
>> `if s.isascii() and s.isdigit():`
>>
>> I want to add it in Python 3.7 if there are no opposite opinions.
>>
> 
> I'm not sure that the decimal-digit check is actually improved by
> this, but nonetheless, I am in favour of this feature. In CPython,
> this method can simply look at the object headers to see if it has the
> 'ascii' flag set; otherwise, it'd be effectively equivalent to:
> 
> def isascii(self):
>     return ord(max(self)) < 128
> 
> Would be handy when working with semi-textual protocols, where ASCII
> text is trivially encoded, but non-ASCII text may require negotiation
> or a protocol header.

+1

Just a note: checking the header in CPython will only give a hint,
since strings created using higher order kinds can still be 100%
ASCII.

-- 
Marc-Andre Lemburg
eGenix.com

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