bpo-35631: Improve typing docs wrt abstract/concrete collection types (GH-11396)

scop · ilevkivskyi · commit 31ec52a9afed · 2019-01-04T14:14:32.000Z
https://bugs.python.org/issue35631
diff --git a/Doc/library/typing.rst b/Doc/library/typing.rst
@@ -50,20 +50,20 @@ A type alias is defined by assigning the type to the alias. In this example,
 
 Type aliases are useful for simplifying complex type signatures. For example::
 
-   from typing import Dict, Tuple, List
+   from typing import Dict, Tuple, Sequence
 
    ConnectionOptions = Dict[str, str]
    Address = Tuple[str, int]
    Server = Tuple[Address, ConnectionOptions]
 
-   def broadcast_message(message: str, servers: List[Server]) -> None:
+   def broadcast_message(message: str, servers: Sequence[Server]) -> None:
        ...
 
    # The static type checker will treat the previous type signature as
    # being exactly equivalent to this one.
    def broadcast_message(
            message: str,
-           servers: List[Tuple[Tuple[str, int], Dict[str, str]]]) -> None:
+           servers: Sequence[Tuple[Tuple[str, int], Dict[str, str]]]) -> None:
        ...
 
 Note that ``None`` as a type hint is a special case and is replaced by
@@ -568,6 +568,10 @@ The module defines the following classes, functions and decorators:
 .. class:: Mapping(Sized, Collection[KT], Generic[VT_co])
 
     A generic version of :class:`collections.abc.Mapping`.
+    This type can be used as follows::
+
+      def get_position_in_index(word_list: Mapping[str, int], word: str) -> int:
+          return word_list[word]
 
 .. class:: MutableMapping(Mapping[KT, VT])
 
@@ -601,8 +605,8 @@ The module defines the following classes, functions and decorators:
 
    Generic version of :class:`list`.
    Useful for annotating return types. To annotate arguments it is preferred
-   to use abstract collection types such as :class:`Mapping`, :class:`Sequence`,
-   or :class:`AbstractSet`.
+   to use an abstract collection type such as :class:`Sequence` or
+   :class:`Iterable`.
 
    This type may be used as follows::
 
@@ -617,6 +621,8 @@ The module defines the following classes, functions and decorators:
 .. class:: Set(set, MutableSet[T])
 
    A generic version of :class:`builtins.set <set>`.
+   Useful for annotating return types. To annotate arguments it is preferred
+   to use an abstract collection type such as :class:`AbstractSet`.
 
 .. class:: FrozenSet(frozenset, AbstractSet[T_co])
 
@@ -678,10 +684,13 @@ The module defines the following classes, functions and decorators:
 .. class:: Dict(dict, MutableMapping[KT, VT])
 
    A generic version of :class:`dict`.
-   The usage of this type is as follows::
+   Useful for annotating return types. To annotate arguments it is preferred
+   to use an abstract collection type such as :class:`Mapping`.
 
-      def get_position_in_index(word_list: Dict[str, int], word: str) -> int:
-          return word_list[word]
+   This type can be used as follows::
+
+      def count_words(text: str) -> Dict[str, int]:
+          ...
 
 .. class:: DefaultDict(collections.defaultdict, MutableMapping[KT, VT])
 
