Why a class with @pinject.inject is always singleton? Is it a bug?

[alexander-myltsev]

OS: macOS 10.14.5
Python: 3.7
Dependencies:

[tool.poetry.dependencies]
python = "^3.6"
numpy = "^1.16"
PyContracts = "^1.8"
quandl = "^3.4"
pandas = "^0.24"
pinject = "^0.14.1"
typing_extensions = "^3.7"

[tool.poetry.dev-dependencies]
freezegun = "^0.3.11"
pytest = "^4.5"
PyHamcrest = "^1.9"
flake8 = "^3.7"
codecov = "^2.0"
pytest-cov = "^2.7"
jupyterlab = "^0.35.6"
nbval = "^0.9.1"
mypy = "^0.701.0"
pytype = "^2019.5"

Thank you for the lib. I enjoy your design decisions which make it the closest thing to dependency injection in Python I've seen so far. I'd like to use it. But have a problem in the code as follows:

class MyRegistry:
    def reg(self):
        return 42

class FooClass:
    @pinject.inject(['my_registry']) # https://github.com/google/pinject/blob/1e785b550cad4d4f9fd7f60a7d047dab9f7410e0/pinject/bindings.py#L168 make the FooClass singleton 
    def __init__(self, my_registry, param):
        self.my_registry = my_registry
        self.param = param

class MainClass:
    def __init__(self, provide_foo_class):
        a = provide_foo_class(param=1)
        b = provide_foo_class(param=2) # this line gets FooClass instance from the cache since it's singleton 
        print(a.my_registry.reg()) # works fine
        print(b.my_registry.reg()) # obivously, works fine too
        print(a.param)
        print(b.param) # this is actually `a` instance, so it prints 1 instead of 2

if __name__ == '__main__':
    obj_graph = pinject.new_object_graph()
    obj_graph.provide(MainClass)

I tried to override FooClass scope in custom spec, but it throws the exception of ambiguity since FooClass is registered as singleton. I can work around it with the FooClassFactory that creates instances of FooClass, but it seems unnecessary when there is provide_ facility.

How to make it work properly?

[miguelgflores-fever]

By default Pinject uses singleton, you can specify PROTOTYPE as scope.

Pinject has two built-in scopes. Singleton scope (SINGLETON) is the default and always caches. Prototype scope (PROTOTYPE) is the other built-in option and does no caching whatsoever.

Every binding is associated with a scope. You can specify a scope for a binding by decorating a provider method with @in_scope(), or by passing an in_scope arg to bind() in a binding spec's configure() method.

https://github.com/google/pinject/blob/master/README.rst#scopes

[mxab]

I'm facing the same issue.
I tried to make it as prototype in a spec but then I get an ConflictingExplicitBindingsError when I do it like this:

class MyRegistry:
    def reg(self):
        return 42


class FooClass:
    @pinject.inject(['my_registry'])
    def __init__(self, my_registry, param):
        self.my_registry = my_registry
        self.param = param


class MainClass:
    def __init__(self, provide_foo_class):
        a = provide_foo_class(param=1)
        b = provide_foo_class(param=2)

        assert a.param != b.param


class MyBindingSpec(pinject.BindingSpec):
    def configure(self, bind):
        bind('foo_class', to_class=FooClass, in_scope=pinject.PROTOTYPE)


if __name__ == '__main__':
    obj_graph = pinject.new_object_graph(binding_specs=[MyBindingSpec()])
    obj_graph.provide(MainClass)

Traceback (most recent call last):
  File "/home/mafr/.pyenv/versions/3.6.10/lib/python3.6/runpy.py", line 193, in _run_module_as_main
    "__main__", mod_spec)
  File "/home/mafr/.pyenv/versions/3.6.10/lib/python3.6/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "/home/mafr/git/pinject-demo/pinject_demo/__main__.py", line 113, in <module>
    obj_graph = pinject.new_object_graph(binding_specs=[MyBindingSpec()])
  File "/home/mafr/.cache/pypoetry/virtualenvs/pinject-demo-IwpV6JDg-py3.6/lib/python3.6/site-packages/pinject/object_graph.py", line 154, in new_object_graph
    raise e
  File "/home/mafr/.cache/pypoetry/virtualenvs/pinject-demo-IwpV6JDg-py3.6/lib/python3.6/site-packages/pinject/object_graph.py", line 148, in new_object_graph
    [implicit_class_bindings, explicit_bindings]))
  File "/home/mafr/.cache/pypoetry/virtualenvs/pinject-demo-IwpV6JDg-py3.6/lib/python3.6/site-packages/pinject/bindings.py", line 94, in get_overall_binding_key_to_binding_maps
    bindings, handle_binding_collision_fn))
  File "/home/mafr/.cache/pypoetry/virtualenvs/pinject-demo-IwpV6JDg-py3.6/lib/python3.6/site-packages/pinject/bindings.py", line 70, in _get_binding_key_to_binding_maps
    collided_binding_key_to_bindings)
  File "/home/mafr/.cache/pypoetry/virtualenvs/pinject-demo-IwpV6JDg-py3.6/lib/python3.6/site-packages/pinject/bindings.py", line 49, in _handle_explicit_binding_collision
    [colliding_binding, other_binding])
pinject.errors.ConflictingExplicitBindingsError: multiple explicit bindings for same binding name:
  the binding at <decorator-gen-2>:235, from the binding name "foo_class" (unannotated) to the provider method pinject.bindings.provide_it at <decorator-gen-2>:235, in "prototype scope" scope
  the binding at /home/mafr/git/pinject-demo/pinject_demo/__main__.py:92, from the binding name "foo_class" (unannotated) to the class __main__.FooClass at /home/mafr/git/pinject-demo/pinject_demo/__main__.py:92, in "singleton scope" scope