Incorrect check on string interpolation

[dmoisset]

When sending this type-correct code

d = {"greeting": "hello", "count": 10}
print("%(greeting)s World. %(count)d%% tests failing" % d)

through mypy, I get the following:

error: String interpolation mixes specifier with and without mapping keys

Which should be accepted; the only interpolator I'm using withot keys is "%%" which is just an escape and can not cause problems

[ddfisher]

This does look like it's related to the %%. Here's a slightly reduced repro: "%(foo)s %%" % {"foo": "foo"}

[fabianhjr]

Ok, so basically this has to do with a regex in parse_conversion_specifiers(self, format: str) -> List[ConversionSpecifier]: in checkstrformat.py.

Overall, I have been researching and %% should be an escape character, so this is what I think should be done:

Prepend (?:%%)| to the regex to catch the escape.

EDIT: Testing this change returns empty matches; Should be easier to filter out.

[gvanrossum]

Wanna add tests and submit a PR?

On Monday, July 18, 2016, Fabian Heredia Montiel [email protected]
wrote:

Ok, so basically this has to do with a regex in parse_conversion_specifiers(self,
format: str) -> List[ConversionSpecifier]: in checkstrformat.py.

Overall, I have been researching and %% should be an escape character, so
this is what I think should be done:

Prepend (?:%%)| to the regex to catch the escape.

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[fabianhjr]

Working on it; if I get it to pass locally I will open a PR.