Make dict hint more useful in normal case

hypothesis-python/docs/details.rst

@@ -568,6 +568,13 @@ up our type hints.
     which is otherwise backwards-compatible.  We often omit type hints for
     deprecated features or arguments, as an additional form of warning.
 
+There are known issues inferring the type of examples generated by
+:func:`~hypothesis.strategies.deferred`, :func:`~hypothesis.strategies.recursive`,
+:func:`~hypothesis.strategies.one_of`, :func:`~hypothesis.strategies.dictionaries`,
+and :func:`~hypothesis.strategies.fixed_dictionaries`.
+We will fix these, and require correspondingly newer versions of Mypy for type
+hinting, as the ecosystem improves.
+
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 Writing downstream type hints
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

hypothesis-python/src/hypothesis/strategies.py

@@ -80,7 +80,7 @@
     from random import Random  # noqa
     from typing import Any, Dict, Union, Sequence, Callable, Pattern  # noqa
     from typing import TypeVar, Tuple, List, Set, FrozenSet, overload  # noqa
-    from typing import Type, Mapping, Text, AnyStr, Optional  # noqa
+    from typing import Type, Text, AnyStr, Optional  # noqa
 
     from hypothesis.utils.conventions import InferType  # noqa
     from hypothesis.searchstrategy.strategies import T, Ex  # noqa
@@ -716,7 +716,7 @@ def iterables(elements=None, min_size=None, average_size=None, max_size=None,
 
 @defines_strategy
 def fixed_dictionaries(
-    mapping  # type: Mapping[T, SearchStrategy[Ex]]
+    mapping  # type: Dict[T, SearchStrategy[Ex]]
 ):
     # type: (...) -> SearchStrategy[Dict[T, Ex]]
     """Generates a dictionary of the same type as mapping with a fixed set of
@@ -746,7 +746,9 @@ def dictionaries(
     average_size=None,  # type: int
     max_size=None,  # type: int
 ):
-    # type: (...) -> SearchStrategy[Mapping[Ex, T]]
+    # type: (...) -> SearchStrategy[Dict[Ex, T]]
+    # Describing the exact dict_class to Mypy drops the key and value types,
+    # so we report Dict[K, V] instead of Mapping[Any, Any] for now.  Sorry!
     """Generates dictionaries of type dict_class with keys drawn from the keys
     argument and values drawn from the values argument.
 

whole-repo-tests/test_type_hints.py

@@ -54,14 +54,12 @@ def get_mypy_analysed_type(fname, val):
     ('integers().map(str)', 'str'),
     ('booleans().filter(bool)', 'bool'),
     ('lists(none())', 'list[None]'),
-    ('dictionaries(integers(), datetimes())',
-     'typing.Mapping[int, datetime.datetime]'),
+    ('dictionaries(integers(), datetimes())', 'dict[int, datetime.datetime]'),
     ('recursive(integers(), lists)', 'Union[list[Ex`-1], int]'),
     # Mypy might not resolve deferred strategies, but it doesn't error either.
     ('deferred(lambda: integers() | lists(s))', 'Any'),
-    # Note: this *should* give 'Union[int, str]' (or Text), but Mypy doesn't
-    # cope with finding the union of the parameter types.
-    # If or when this changes, fix the hints on `one_of` too!
+    # See https://github.com/python/mypy/issues/5269 - fix the hints on
+    # `one_of` and document the minimum Mypy version when the issue is fixed.
     ('one_of(integers(), text())', 'Any'),
 ])
 def test_revealed_types(tmpdir, val, expect):