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Merged
davidparsson merged 2 commits into from
Jan 9, 2026
Merged

Use covariant types for multibind collections/mappings #307

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fb10e3a
Use covariant types in multibind
davidparsson Jan 9, 2026
1589f3f
test: Multibind a tuple
davidparsson Jan 9, 2026
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10 changes: 6 additions & 4 deletions injector/__init__.py
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Original file line number Diff line number Diff line change
Expand Up @@ -27,11 +27,13 @@
TYPE_CHECKING,
Any,
Callable,
Collection,
Dict,
Generator,
Generic,
Iterable,
List,
Mapping,
Optional,
Set,
Tuple,
Expand Down Expand Up @@ -387,7 +389,7 @@ def multibind(
element_type = get_args(_punch_through_alias(interface))[0]
except IndexError:
raise InvalidInterface(f"Use typing.List[T] or list[T] to specify the element type of the list")
if isinstance(to, list):
if isinstance(to, Collection):
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Copilot AI Jan 9, 2026

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Using isinstance(to, Collection) will incorrectly match strings since strings are collections in Python. This could cause the code to iterate over individual characters instead of treating the string as an invalid input. Add an explicit check to exclude strings: if isinstance(to, Collection) and not isinstance(to, (str, bytes)):

Suggested change
if isinstance(to, Collection):
if isinstance(to, Collection) and not isinstance(to, (str, bytes)):

Copilot uses AI. Check for mistakes.
for element in to:
element_binding = self._binder.create_binding(element_type, element, scope)
self.append(element_binding.provider, element_binding.scope)
Expand Down Expand Up @@ -415,7 +417,7 @@ def multibind(
raise InvalidInterface(
f"Use typing.Dict[K, V] or dict[K, V] to specify the value type of the dict"
)
if isinstance(to, dict):
if isinstance(to, Mapping):
for key, value in to.items():
element_binding = self._binder.create_binding(value_type, value, scope)
self.append(KeyValueProvider(key, element_binding.provider), element_binding.scope)
Expand Down Expand Up @@ -544,7 +546,7 @@ def bind(
def multibind(
self,
interface: Type[List[T]],
to: Union[List[Union[T, Type[T]]], Callable[..., List[T]], Provider[List[T]], Type[T]],
to: Union[Collection[Union[T, Type[T]]], Callable[..., List[T]], Provider[List[T]], Type[T]],
scope: Union[Type['Scope'], 'ScopeDecorator', None] = None,
) -> None: # pragma: no cover
pass
Expand All @@ -553,7 +555,7 @@ def multibind(
def multibind(
self,
interface: Type[Dict[K, V]],
to: Union[Dict[K, Union[V, Type[V]]], Callable[..., Dict[K, V]], Provider[Dict[K, V]]],
to: Union[Mapping[K, Union[V, Type[V]]], Callable[..., Dict[K, V]], Provider[Dict[K, V]]],
scope: Union[Type['Scope'], 'ScopeDecorator', None] = None,
) -> None: # pragma: no cover
pass
Expand Down
8 changes: 7 additions & 1 deletion injector_test.py
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Original file line number Diff line number Diff line change
Expand Up @@ -733,19 +733,25 @@ class PluginD(Plugin):
pass


class PluginE(Plugin):
pass


def test_multibind_list_of_plugins():
def configure(binder: Binder):
binder.multibind(List[Plugin], to=PluginA)
binder.multibind(List[Plugin], to=[PluginB, PluginC()])
binder.multibind(List[Plugin], to=lambda: [PluginD()])
binder.multibind(List[Plugin], to=(PluginE,))

injector = Injector([configure])
plugins = injector.get(List[Plugin])
assert len(plugins) == 4
assert len(plugins) == 5
assert isinstance(plugins[0], PluginA)
assert isinstance(plugins[1], PluginB)
assert isinstance(plugins[2], PluginC)
assert isinstance(plugins[3], PluginD)
assert isinstance(plugins[4], PluginE)


def test_multibind_dict_of_plugins():
Expand Down