Create unique types for UniqueIdentifiers

(so Mypy can tell you're using the wrong one)

hypothesis-python/src/hypothesis/core.py

@@ -76,7 +76,7 @@
 
 if False:
     from typing import Any, Dict, Callable, Optional, Union  # noqa
-    from hypothesis.utils.conventions import UniqueIdentifier  # noqa
+    from hypothesis.utils.conventions import InferType  # noqa
 
 
 running_under_pytest = False
@@ -894,8 +894,8 @@ def fake_subTest(self, msg=None, **__):
 
 
 def given(
-    *given_arguments,  # type: Union[SearchStrategy, UniqueIdentifier]
-    **given_kwargs  # type: Union[SearchStrategy, UniqueIdentifier]
+    *given_arguments,  # type: Union[SearchStrategy, InferType]
+    **given_kwargs  # type: Union[SearchStrategy, InferType]
 ):
     # type: (...) -> Callable[[Callable[..., None]], Callable[..., None]]
     """A decorator for turning a test function that accepts arguments into a

hypothesis-python/src/hypothesis/extra/django/models.py

@@ -34,11 +34,11 @@
 from hypothesis.extra.pytz import timezones
 from hypothesis.provisional import emails, ip4_addr_strings, \
     ip6_addr_strings
-from hypothesis.utils.conventions import UniqueIdentifier
+from hypothesis.utils.conventions import DefaultValueType, default_value
 
 if False:
     from datetime import tzinfo  # noqa
-    from typing import Any, Type, Optional, List, Text, Callable, Union  # noqa
+    from typing import Any, Dict, Type, Optional, List, Text, Callable, Union  # noqa
 
 
 def get_tz_strat():
@@ -94,9 +94,6 @@ def add_default_field_mapping(field_type, strategy):
     field_mappings()[field_type] = strategy
 
 
-default_value = UniqueIdentifier(u'default_value')
-
-
 def validator_to_filter(f):
     # type: (Type[dm.Field]) -> Callable[[Any], bool]
     """Converts the field run_validators method to something suitable for use
@@ -171,7 +168,7 @@ def _get_strategy_for_field(f):
 
 def models(
     model,  # type: Type[dm.Model]
-    **field_strategies  # type: Union[st.SearchStrategy[Any], UniqueIdentifier]
+    **field_strategies  # type: Union[st.SearchStrategy[Any], DefaultValueType]
 ):
     # type: (...) -> st.SearchStrategy[Any]
     """Return a strategy for examples of ``model``.
@@ -199,8 +196,10 @@ def models(
 
       shop_strategy = models(Shop, company=models(Company))
     """
-    result = {k: v for k, v in field_strategies.items()
-              if v is not default_value}
+    result = {}
+    for k, v in field_strategies.items():
+        if not isinstance(v, DefaultValueType):
+            result[k] = v
     missed = []  # type: List[Text]
     for f in model._meta.concrete_fields:
         if not (f.name in field_strategies or isinstance(f, dm.AutoField)):

hypothesis-python/src/hypothesis/strategies.py

@@ -52,7 +52,7 @@
     from typing import TypeVar, Tuple, List, Set, FrozenSet, overload  # noqa
     from typing import Type, Mapping, Text, AnyStr, Optional  # noqa
 
-    from hypothesis.utils.conventions import UniqueIdentifier  # noqa
+    from hypothesis.utils.conventions import InferType  # noqa
     from hypothesis.searchstrategy.strategies import T, Ex  # noqa
     K, V = TypeVar['K'], TypeVar['V']
     # See https://github.com/python/mypy/issues/3186 - numbers.Real is wrong!
@@ -1024,7 +1024,7 @@ def do_draw(self, data):
 @defines_strategy
 def builds(
     *callable_and_args,  # type: Any
-    **kwargs  # type: Union[SearchStrategy[Any], UniqueIdentifier]
+    **kwargs  # type: Union[SearchStrategy[Any], InferType]
 ):
     # type: (...) -> SearchStrategy[Any]
     """Generates values by drawing from ``args`` and ``kwargs`` and passing

hypothesis-python/src/hypothesis/utils/conventions.py

@@ -27,5 +27,15 @@ def __repr__(self):
         return self.identifier
 
 
-infer = UniqueIdentifier(u'infer')
+class DefaultValueType(UniqueIdentifier):
+    # Using subclasses so they can be distinguished by e.g. Mypy
+    pass
+
+
+class InferType(UniqueIdentifier):
+    pass
+
+
 not_set = UniqueIdentifier(u'not_set')
+default_value = DefaultValueType(u'default_value')
+infer = InferType(u'infer')