Add "everything but" recipe using from_type

hypothesis-python/RELEASE.rst

@@ -0,0 +1,5 @@
+RELEASE_TYPE: patch
+
+Adds a recipe to the docstring of :func:`~hypothesis.strategies.from_type`
+that describes a means for drawing values for "everything except" a specified type.
+This recipe is especially useful for writing tests that perform input-type validation.

hypothesis-python/src/hypothesis/_strategies.py

@@ -1305,6 +1305,25 @@ def from_type(thing):
        other elements in the lookup.
     4. Finally, if ``thing`` has type annotations for all required arguments,
        it is resolved via :func:`~hypothesis.strategies.builds`.
+
+    There is a valuable recipe for leveraging ``from_type()`` to generate
+    "everything except" values from a specified type. I.e.
+
+    .. code-block:: python
+
+        def everything_except(excluded_types):
+            return (
+                from_type(type).flatmap(from_type)
+                .filter(lambda x: not isinstance(x, excluded_types))
+            )
+
+     For example, ``everything_except(int)`` returns a strategy that can
+     generate anything that ``from_type()`` can ever generate, except for
+     instances of :class:python:int, and excluding instances of types
+     added via :func:~hypothesis.strategies.register_type_strategy.
+
+     This is useful when writing tests which check that invalid input is
+     rejected in a certain way.
     """
     # TODO: We would like to move this to the top level, but pending some major
     # refactoring it's hard to do without creating circular imports.

hypothesis-python/tests/nocover/test_from_type_recipe.py

@@ -0,0 +1,49 @@
+# coding=utf-8
+#
+# This file is part of Hypothesis, which may be found at
+# https://github.com/HypothesisWorks/hypothesis/
+#
+# Most of this work is copyright (C) 2013-2019 David R. MacIver
+# (david@drmaciver.com), but it contains contributions by others. See
+# CONTRIBUTING.rst for a full list of people who may hold copyright, and
+# consult the git log if you need to determine who owns an individual
+# contribution.
+#
+# This Source Code Form is subject to the terms of the Mozilla Public License,
+# v. 2.0. If a copy of the MPL was not distributed with this file, You can
+# obtain one at https://mozilla.org/MPL/2.0/.
+#
+# END HEADER
+
+from __future__ import absolute_import, division, print_function
+
+import hypothesis.strategies as st
+from hypothesis import given
+from hypothesis.searchstrategy.types import _global_type_lookup
+
+
+def everything_except(excluded_types):
+    """Recipe copied from the docstring of ``from_type``"""
+    return (
+        st.from_type(type)
+        .flatmap(st.from_type)
+        .filter(lambda x: not isinstance(x, excluded_types))
+    )
+
+
+@given(
+    excluded_types=st.lists(
+        st.sampled_from(
+            sorted(
+                [x for x in _global_type_lookup if x.__module__ != "typing"], key=str
+            )
+        ),
+        min_size=1,
+        max_size=3,
+        unique=True,
+    ).map(tuple),
+    data=st.data(),
+)
+def test_recipe_for_everything_except(excluded_types, data):
+    value = data.draw(everything_except(excluded_types))
+    assert not isinstance(value, excluded_types)