bpo-39572: Document ’total’ flag of TypedDict (GH-18554)

3 files changed, 29 insertions, 3 deletions

diff --git a/Doc/library/typing.rst b/Doc/library/typing.rst
index d3bab94c6d..eac75ee865 100644
--- a/Doc/library/typing.rst
+++ b/Doc/library/typing.rst
@@ -996,8 +996,20 @@ The module defines the following classes, functions and decorators:
       Point2D = TypedDict('Point2D', x=int, y=int, label=str)
       Point2D = TypedDict('Point2D', {'x': int, 'y': int, 'label': str})
 
-   See :pep:`589` for more examples and detailed rules of using ``TypedDict``
-   with type checkers.
+   By default, all keys must be present in a TypedDict. It is possible
+   to override this by specifying totality.
+   Usage::
+
+      class point2D(TypedDict, total=False):
+          x: int
+          y: int
+
+   This means that a point2D TypedDict can have any of the keys omitted.A type
+   checker is only expected to support a literal False or True as the value of
+   the total argument. True is the default, and makes all items defined in the
+   class body be required.
+
+   See :pep:`589` for more examples and detailed rules of using ``TypedDict``.
 
    .. versionadded:: 3.8
 
diff --git a/Lib/typing.py b/Lib/typing.py
index 6da145fcdb..0a685d304b 100644
--- a/Lib/typing.py
+++ b/Lib/typing.py
@@ -13,7 +13,7 @@ At large scale, the structure of the module is following:
 * Public helper functions: get_type_hints, overload, cast, no_type_check,
   no_type_check_decorator.
 * Generic aliases for collections.abc ABCs and few additional protocols.
-* Special types: NewType, NamedTuple, TypedDict (may be added soon).
+* Special types: NewType, NamedTuple, TypedDict.
 * Wrapper submodules for re and io related types.
 """
 
@@ -1885,6 +1885,19 @@ class TypedDict(dict, metaclass=_TypedDictMeta):
         Point2D = TypedDict('Point2D', x=int, y=int, label=str)
         Point2D = TypedDict('Point2D', {'x': int, 'y': int, 'label': str})
 
+    By default, all keys must be present in a TypedDict. It is possible
+    to override this by specifying totality.
+    Usage::
+
+        class point2D(TypedDict, total=False):
+            x: int
+            y: int
+
+    This means that a point2D TypedDict can have any of the keys omitted.A type
+    checker is only expected to support a literal False or True as the value of
+    the total argument. True is the default, and makes all items defined in the
+    class body be required.
+
     The class syntax is only supported in Python 3.6+, while two other
     syntax forms work for Python 2.7 and 3.2+
     """
diff --git a/Misc/NEWS.d/next/Documentation/2020-02-18-18-37-07.bpo-39572.CCtzy1.rst b/Misc/NEWS.d/next/Documentation/2020-02-18-18-37-07.bpo-39572.CCtzy1.rst
new file mode 100644
index 0000000000..d47bb455e7
--- /dev/null
+++ b/Misc/NEWS.d/next/Documentation/2020-02-18-18-37-07.bpo-39572.CCtzy1.rst
@@ -0,0 +1 @@
+Updated documentation of ``total`` flag of TypeDict.