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Make string interpolation checking less unnecessarily permissive #2519

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Make string interpolation checking less unnecessarily permissive #2519

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8 changes: 3 additions & 5 deletions mypy/checkstrformat.py
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Original file line number Diff line number Diff line change
Expand Up @@ -151,13 +151,11 @@ def check_simple_str_interpolation(self, specifiers: List[ConversionSpecifier],

def check_mapping_str_interpolation(self, specifiers: List[ConversionSpecifier],
replacements: Expression) -> None:
if (isinstance(replacements, DictExpr) and
all(isinstance(k, (StrExpr, BytesExpr))
for k, v in replacements.items)):
if isinstance(replacements, DictExpr):

@JukkaL JukkaL Dec 2, 2016

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This is generally not right. Consider this example:

x = 'q'
'%(q)d' % {'a': 1, x: 2}   # actually okay

What about still using the all(...) check (include also unicode), but only for the key_not_in_mapping error? Item types can still be checked even if some keys are not literals -- we can assume that there are no duplicate keys.

@JukkaL JukkaL Dec 20, 2016

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What about the case with a non-literal key? It might be pretty rare, but here's one example where it would be kind of reasonable:

# constants.py
key1 = 'key1'
key2 = 'key2'

# code.py
from constants import key1, key2
...
'%(key1)d, %(key2)d' % {key1: 1, key2: 2}

Not sure whether we are likely to encounter code like that in practice.

mapping = {} # type: Dict[str, Type]
for k, v in replacements.items:
key_str = cast(StrExpr, k).value
mapping[key_str] = self.accept(v)
if isinstance(k, (StrExpr, BytesExpr, UnicodeExpr)):
mapping[k.value] = self.accept(v)

for specifier in specifiers:
if specifier.type == '%':
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7 changes: 7 additions & 0 deletions test-data/unit/check-expressions.test
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Expand Up @@ -1083,9 +1083,16 @@ a = None # type: Any
'%(a)d' % {'a': 1, 'b': 2, 'c': 3}
'%(q)d' % {'a': 1, 'b': 2, 'c': 3} # E: Key 'q' not found in mapping
'%(a)d %%' % {'a': 1}
'%(q)d' % {'a': 1, 'b': 2, 0: 3} # E: Key 'q' not found in mapping

[builtins fixtures/dict.pyi]

[case testStringInterpolationMappingKeys_python2]
'%(q)d' % {u'a': 1, 'b': 2, 'c': 3} # E: Key 'q' not found in mapping
'%(a)d' % {u'a': 1, 'b': 2, 'c': 3}

[builtins_py2 fixtures/python2.pyi]

[case testStringInterpolationMappingDictTypes]
from typing import Any, Dict
a = None # type: Any
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8 changes: 7 additions & 1 deletion test-data/unit/fixtures/python2.pyi
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@@ -1,4 +1,4 @@
from typing import Generic, Iterable, TypeVar
from typing import Generic, Iterable, Mapping, TypeVar

class object:
def __init__(self) -> None: pass
Expand All @@ -9,10 +9,16 @@ class type:
class function: pass

class int: pass
class float: pass
class str: pass
class unicode: pass
class tuple: pass

T = TypeVar('T')
class list(Iterable[T], Generic[T]): pass

KT = TypeVar('KT')
VT = TypeVar('VT')
class dict(Iterable[KT], Mapping[KT, VT], Generic[KT, VT]): pass

# Definition of None is implicit