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Merged
JukkaL merged 3 commits into from
May 30, 2017
Merged

Make return type of open() more precise #3477

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c7b8d71
Make return type of open() more precise
May 30, 2017
6883fbb
Fix unit tests
May 30, 2017
0ad330e
Fix unit tests good
May 30, 2017
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7 changes: 3 additions & 4 deletions mypy/funcplugins.py
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Original file line number Diff line number Diff line change
Expand Up @@ -44,7 +44,7 @@ def open_callback(
named_generic_type: Callable[[str, List[Type]], Type]) -> Type:
"""Infer a better return type for 'open'.

Infer IO[str] or IO[bytes] as the return value if the mode argument is not
Infer TextIO or BinaryIO as the return value if the mode argument is not
given or is a literal.
"""
mode = None
Expand All @@ -55,10 +55,9 @@ def open_callback(
if mode is not None:
assert isinstance(inferred_return_type, Instance)
if 'b' in mode:
arg = named_generic_type('builtins.bytes', [])
return named_generic_type('typing.BinaryIO', [])
else:
arg = named_generic_type('builtins.str', [])
return Instance(inferred_return_type.type, [arg])
return named_generic_type('typing.TextIO', [])
return inferred_return_type


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14 changes: 7 additions & 7 deletions test-data/unit/pythoneval.test
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Original file line number Diff line number Diff line change
Expand Up @@ -400,7 +400,7 @@ f.write(b'x')
f.foobar()
[out]
_program.py:3: error: Argument 1 to "write" of "IO" has incompatible type "bytes"; expected "str"
_program.py:4: error: IO[str] has no attribute "foobar"
_program.py:4: error: "TextIO" has no attribute "foobar"

[case testOpenReturnTypeInference]
reveal_type(open('x'))
Expand All @@ -409,9 +409,9 @@ reveal_type(open('x', 'rb'))
mode = 'rb'
reveal_type(open('x', mode))
[out]
_program.py:1: error: Revealed type is 'typing.IO[builtins.str]'
_program.py:2: error: Revealed type is 'typing.IO[builtins.str]'
_program.py:3: error: Revealed type is 'typing.IO[builtins.bytes]'
_program.py:1: error: Revealed type is 'typing.TextIO'
_program.py:2: error: Revealed type is 'typing.TextIO'
_program.py:3: error: Revealed type is 'typing.BinaryIO'
_program.py:5: error: Revealed type is 'typing.IO[Any]'

[case testOpenReturnTypeInferenceSpecialCases]
Expand All @@ -421,10 +421,10 @@ reveal_type(open(file='x', mode='rb'))
mode = 'rb'
reveal_type(open(mode=mode, file='r'))
[out]
_testOpenReturnTypeInferenceSpecialCases.py:1: error: Revealed type is 'typing.IO[builtins.str]'
_testOpenReturnTypeInferenceSpecialCases.py:1: error: Revealed type is 'typing.TextIO'
_testOpenReturnTypeInferenceSpecialCases.py:1: error: Too few arguments for "open"
_testOpenReturnTypeInferenceSpecialCases.py:2: error: Revealed type is 'typing.IO[builtins.bytes]'
_testOpenReturnTypeInferenceSpecialCases.py:3: error: Revealed type is 'typing.IO[builtins.bytes]'
_testOpenReturnTypeInferenceSpecialCases.py:2: error: Revealed type is 'typing.BinaryIO'
_testOpenReturnTypeInferenceSpecialCases.py:3: error: Revealed type is 'typing.BinaryIO'
_testOpenReturnTypeInferenceSpecialCases.py:5: error: Revealed type is 'typing.IO[Any]'

[case testGenericPatterns]
Expand Down