Overload signature of get to return an Optional value and to allow default to take any type to match runtime behavior.

Roy Williams · ambv · commit 6008b9dbb14b · 2017-01-11T22:02:29.000-08:00
This chage more closely matches the behavior of `get` at runtime. Users can pass whatever they want in to the default
parameter and it will be returned if the key is absent. Additionally, `get` should return an `Optional` if called with
only one parameter.

```python
z = {'a': 22}
reveal_type(z.get('b'))
reveal_type(z.get('b', 22))
reveal_type(z.get('b', 'hello'))
```

Before:
```shell
test_get_default.py:2: error: Revealed type is 'builtins.int*'
test_get_default.py:3: error: Revealed type is 'builtins.int*'
test_get_default.py:4: error: Revealed type is 'builtins.int*'
test_get_default.py:4: error: Argument 2 to "get" of "dict" has incompatible type "str"; expected "int"
```

After:
```shell
test_get_default.py:2: error: Revealed type is 'Union[builtins.int*, builtins.None]'
test_get_default.py:3: error: Revealed type is 'builtins.int'
test_get_default.py:4: error: Revealed type is 'Union[builtins.int, builtins.str*]'
```
diff --git a/stdlib/2/__builtin__.pyi b/stdlib/2/__builtin__.pyi
@@ -538,7 +538,10 @@ class dict(MutableMapping[_KT, _VT], Generic[_KT, _VT]):
 def has_key(self, k: _KT) -> bool: ...
 def clear(self) -> None: ...
 def copy(self) -> Dict[_KT, _VT]: ...
- def get(self, k: _KT, default: _VT = None) -> _VT: ...
+ @overload
+ def get(self, k: _KT) -> Optional[_VT]: ...
+ @overload
+ def get(self, k: _KT, default: _T) -> Union[_VT, _T]: ...
 def pop(self, k: _KT, default: _VT = ...) -> _VT: ...
 def popitem(self) -> Tuple[_KT, _VT]: ...
 def setdefault(self, k: _KT, default: _VT = ...) -> _VT: ...
diff --git a/stdlib/2/typing.pyi b/stdlib/2/typing.pyi
@@ -174,15 +174,17 @@ class ValuesView(MappingView, Iterable[_VT_co], Generic[_VT_co]):
 def __contains__(self, o: object) -> bool: ...
 def __iter__(self) -> Iterator[_VT_co]: ...
 
-class Mapping(Sized, Iterable[_KT], Container[_KT], Generic[_KT, _VT_co]):
+class Mapping(Iterable[_KT], Container[_KT], Sized, Generic[_KT, _VT_co]):
 # TODO: We wish the key type could also be covariant, but that doesn't work,
 # see discussion in https: //github.com/python/typing/pull/273.
 @abstractmethod
 def __getitem__(self, k: _KT) -> _VT_co:
 ...
 # Mixin methods
- def get(self, k: _KT, default: _VT_co = ...) -> _VT_co: # type: ignore
- ...
+ @overload # type: ignore
+ def get(self, k: _KT) -> Optional[_VT_co]: ...
+ @overload # type: ignore
+ def get(self, k: _KT, default: _T) -> Union[_VT_co, _T]: ...
 def keys(self) -> list[_KT]: ...
 def values(self) -> list[_VT_co]: ...
 def items(self) -> list[Tuple[_KT, _VT_co]]: ...
diff --git a/stdlib/3/builtins.pyi b/stdlib/3/builtins.pyi
@@ -556,7 +556,10 @@ class dict(MutableMapping[_KT, _VT], Generic[_KT, _VT]):
 def __init__(self, iterable: Iterable[Tuple[_KT, _VT]], **kwargs: _VT) -> None: ...
 def clear(self) -> None: ...
 def copy(self) -> Dict[_KT, _VT]: ...
- def get(self, k: _KT, default: _VT = None) -> _VT: ...
+ @overload
+ def get(self, k: _KT) -> Optional[_VT]: ...
+ @overload
+ def get(self, k: _KT, default: _T) -> Union[_VT, _T]: ...
 def pop(self, k: _KT, default: _VT = None) -> _VT: ...
 def popitem(self) -> Tuple[_KT, _VT]: ...
 def setdefault(self, k: _KT, default: _VT = None) -> _VT: ...
diff --git a/stdlib/3/typing.pyi b/stdlib/3/typing.pyi
@@ -250,8 +250,10 @@ class Mapping(Iterable[_KT], Container[_KT], Sized, Generic[_KT, _VT_co]):
 def __getitem__(self, k: _KT) -> _VT_co:
 ...
 # Mixin methods
- def get(self, k: _KT, default: _VT_co = ...) -> _VT_co: # type: ignore
- ...
+ @overload # type: ignore
+ def get(self, k: _KT) -> Optional[_VT_co]: ...
+ @overload # type: ignore
+ def get(self, k: _KT, default: _T) -> Union[_VT_co, _T]: ...
 def items(self) -> AbstractSet[Tuple[_KT, _VT_co]]: ...
 def keys(self) -> AbstractSet[_KT]: ...
 def values(self) -> ValuesView[_VT_co]: ...

-Original file line number
+Diff line change
 defhas_key(self, k: _KT) ->bool: ...
 defclear(self) ->None: ...
 defcopy(self) ->Dict[_KT, _VT]: ...
 -defget(self, k: _KT, default: _VT=None) ->_VT: ...
 +@overload
 +defget(self, k: _KT) ->Optional[_VT]: ...
 +@overload
 +defget(self, k: _KT, default: _T) ->Union[_VT, _T]: ...
 defpop(self, k: _KT, default: _VT= ...) ->_VT: ...
 defpopitem(self) ->Tuple[_KT, _VT]: ...
 defsetdefault(self, k: _KT, default: _VT= ...) ->_VT: ...
-Original file line number
+Diff line change
 def__contains__(self, o: object) ->bool: ...
 def__iter__(self) ->Iterator[_VT_co]: ...
 -classMapping(Sized, Iterable[_KT], Container[_KT], Generic[_KT, _VT_co]):
 +classMapping(Iterable[_KT], Container[_KT], Sized, Generic[_KT, _VT_co]):
 # TODO: We wish the key type could also be covariant, but that doesn't work,
 # see discussion in https: //github.com/python/typing/pull/273.
 @abstractmethod
 def__getitem__(self, k: _KT) ->_VT_co:
  ...
 # Mixin methods
 -defget(self, k: _KT, default: _VT_co= ...) ->_VT_co: # type: ignore
 - ...
 +@overload# type: ignore
 +defget(self, k: _KT) ->Optional[_VT_co]: ...
 +@overload# type: ignore
 +defget(self, k: _KT, default: _T) ->Union[_VT_co, _T]: ...
 defkeys(self) ->list[_KT]: ...
 defvalues(self) ->list[_VT_co]: ...
 defitems(self) ->list[Tuple[_KT, _VT_co]]: ...