8000 Allow class-based TypedDicts in all python versions by msullivan · Pull Request #6971 · python/mypy · GitHub
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Allow class-based TypedDicts in all python versions #6971

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Merged
merged 1 commit into from
Jun 11, 2019
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Allow class-based TypedDicts in all python versions #6971

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Allow class-based TypedDicts in all python versions 
Entries can't be *declared* in versions that don't support type
annotations, of course, but class-based TypedDict still serves a
valuable purpose in merging TypedDicts together.

This error *only* triggers on empty TypedDicts, since any non-empty
ones would have failed earlier with a syntax error. So there is no
reason to prohibit it because we can handle that case totally fine.
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@msullivan
msullivan committed Jun 11, 2019
commit 38ca59935b167089eb06e812c9a3ace2e5ee09fc
3 changes: 0 additions & 3 deletions mypy/newsemanal/semanal_typeddict.py
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Expand Up @@ -120,9 +120,6 @@ def analyze_typeddict_classdef_fields(
* List of types for each key
* Set of required keys
"""
if self.options.python_version < (3, 6):
self.fail('TypedDict class syntax is only supported in Python 3.6', defn)
return [], [], set()
fields = [] # type: List[str]
types = [] # type: List[Type]
for stmt in defn.defs.body:
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3 changes: 0 additions & 3 deletions mypy/semanal_typeddict.py
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Expand Up @@ -102,9 +102,6 @@ def check_typeddict_classdef(self, defn: ClassDef,
oldfields: Optional[List[str]] = None) -> Tuple[List[str],
List[Type],
Set[str]]:
if self.options.python_version < (3, 6):
self.fail('TypedDict class syntax is only supported in Python 3.6', defn)
return [], [], set()
fields = [] # type: List[str]
types = [] # type: List[Type]
for stmt in defn.defs.body:
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23 changes: 20 additions & 3 deletions test-data/unit/check-typeddict.test
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Expand Up @@ -128,16 +128,33 @@ reveal_type(p) # E: Revealed type is 'TypedDict('__main__.EmptyDict', {})'
[builtins fixtures/dict.pyi]


-- Define TypedDict (Class syntax errors)

[case testCanCreateTypedDictWithClassOldVersion]
# flags: --python-version 3.5

# Test that we can use class-syntax to merge TypedDicts even in
# versions without type annotations

from mypy_extensions import TypedDict

class Point(TypedDict): # E: TypedDict class syntax is only supported in Python 3.6
MovieBase1 = TypedDict(
'MovieBase1', {'name': str, 'year': int})
MovieBase2 = TypedDict(
'MovieBase2', {'based_on': str}, total=False)

class Movie(MovieBase1, MovieBase2):
pass

def foo(x):
# type: (Movie) -> None
pass

foo({}) # E: Keys ('name', 'year') missing for TypedDict "Movie"
foo({'name': 'lol', 'year': 2009, 'based_on': 0}) # E: Incompatible types (expression has type "int", TypedDict item "based_on" has type "str")

[builtins fixtures/dict.pyi]

-- Define TypedDict (Class syntax errors)

[case testCannotCreateTypedDictWithClassOtherBases]
# flags: --python-version 3.6
from mypy_extensions import TypedDict
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