The 'is' operator and check-code

[Martin Geisler]

Adrian Buehlmann <adrian at cadifra.com> writes:

> On 16.11.2010 20:40, Matt Mackall wrote:
>> I'm throwing this out in case any Python experts have opinions.
>> 
>> The 'is' operator is used in a bunch of places as a synonym for ==.
>> This happens to work with short strings and small integers (0 to 256)
>> in CPython, but that's by no means guaranteed by the language, so
>> there are places where we're just getting lucky. So I propose we
>> disallow using it for anything that's not one of the True/False/None
>> singletons. Here's my regex hack:
>> 
>> diff -r 340c46028ebd contrib/check-code.py
>> --- a/contrib/check-code.py	Tue Nov 16 12:55:07 2010 -0600
>> +++ b/contrib/check-code.py	Tue Nov 16 13:35:04 2010 -0600
>> @@ -130,6 +130,7 @@
>>      (r'[\x80-\xff]', "non-ASCII character literal"),
>>      (r'("\')\.format\(', "str.format() not available in Python 2.4"),
>>      (r'^\s*with\s+', "with not available in Python 2.4"),
>> +    (r' is\s+(not\s+)?[^TFNn]', "object comparison with non-singleton"),
>>      (r'(?<!def)\s+(any|all|format)\(',
>>       "any/all/format not available in Python 2.4"),
>>      (r'(?<!def)\s+(callable)\(',
>> 
>
> and elsewhere:
>
> On 17.11.2010 09:05, Martin Geisler wrote:
>> Mads Kiilerich <mads at kiilerich.com> writes:
>>
>>> I won't claim to be a Python expert, but I don't think the
>>> check-code check proposed by Matt is a good idea. It can't be made
>>> reliable - unless we say that all uses of 'is' has to be
>>> white-listed somehow.
>>
>> I propose that we just blacklist using of 'is' with string and
>> numeric literals. That would be something like this:
>>
>>   (r''' is\s+(not\s+)?["'0-9]''', "object comparison with literal"),
>
> Would it be possible to catch negative numbers too?

Good idea, inserting '-' at the end of the range will do that.

I'll wait for feedback from Matt and Dan.

-- 
Martin Geisler

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