Bug adding handler in case of decoration + class function + filtered event

[sdesrozis]

🐛 Bug description

I would like to report a bug using handler defined by decorated function in a class with filtered event.

The following code reproduces all possible situations to add an handler defined w/wo decoration in a class or not, w/wo engine (or args), using an event w/wo filter

engine = Engine(lambda e, b: b)

# decorator
def decorated(fun):
    @functools.wraps(fun)
    def wrapper(*args, **kwargs):
        return fun(*args, **kwargs)
    return wrapper

# handler as a function
def foo():
    print("foo")

# handler as a decorated function
@decorated
def decorated_foo():
    print("decorated_foo")

# register handler as a function -- OK
engine.add_event_handler(Events.EPOCH_STARTED, foo)
# register handler as a function with filter -- OK
engine.add_event_handler(Events.EPOCH_STARTED(every=2), foo)
# register handler as a decorated function -- OK
engine.add_event_handler(Events.EPOCH_STARTED, decorated_foo)
# register handler as a decorated function with filter -- OK
engine.add_event_handler(Events.EPOCH_STARTED(every=2), decorated_foo)


# handler as a function with engine (here args)
def foo_args(args):
    print("foo_args", args)


# handler as a decorated function with engine 
@decorated
def decorated_foo_args(args):
    print("decorated_foo_args", args)

# register handler as a function with engine  -- OK
engine.add_event_handler(Events.EPOCH_STARTED, foo_args)
# register handler as a function with engine and filter -- OK
engine.add_event_handler(Events.EPOCH_STARTED(every=2), foo_args)
# register handler as a decorated function with engine -- OK
engine.add_event_handler(Events.EPOCH_STARTED, decorated_foo_args)
# register handler as a decorated function with engine and filter -- OK
engine.add_event_handler(Events.EPOCH_STARTED(every=2), decorated_foo_args)

class Foo:
    # handler as a class function (ie method)
    def foo(self):
        print("foo")

    # handler as a decorated method
    @decorated
    def decorated_foo(self):
        print("decorated_foo")

    # handler as a method with engine
    def foo_args(self, args):
        print("foo_args", args)

    # handler as a decorated method with engine
    @decorated
    def decorated_foo_args(self, args):
        print("decorated_foo_args", args)


foo = Foo()

# register handler as a method -- OK
engine.add_event_handler(Events.EPOCH_STARTED, foo.foo)
# register handler as a method with filter -- OK
engine.add_event_handler(Events.EPOCH_STARTED(every=2), foo.foo)
# register handler as a decorated method -- OK
engine.add_event_handler(Events.EPOCH_STARTED, foo.decorated_foo)
# register handler as a decorated method with filter -- OK
engine.add_event_handler(Events.EPOCH_STARTED(every=2), foo.decorated_foo)
# register handler as a method with engine  -- OK
engine.add_event_handler(Events.EPOCH_STARTED, foo.foo_args)
# register handler as a method with engine and filter -- OK
engine.add_event_handler(Events.EPOCH_STARTED(every=2), foo.foo_args)
# register handler as a decorated method with engine -- OK
engine.add_event_handler(Events.EPOCH_STARTED, foo.decorated_foo_args)

# register handler as a decorated method with engine and filter -- FAILED
engine.add_event_handler(Events.EPOCH_STARTED(every=2), foo.decorated_foo_args)

engine.run([0])

The error is

Error adding <function Foo.decorated_foo_args at 0x1229b6af0> 'handler': takes parameters ['self', 'args'] but will be called with [](missing a required argument: 'self').

Why ?

First, a handler defined with a filtered event is wrapped with decoration. See https://github.com/sdesrozis/ignite/blob/93be57aa3f71ce601391d59096c3b430c4d9487b/ignite/engine/engine.py#L198. Note that functools.wraps is used to fit the signature of the related handler.

The failed case is decorated method with engine. So, I guess functools.wraps works perfectly and catch self and engine as arguments. But the signature checking search (using inspect.signature) fails because missing self...

See signature checking

ignite/ignite/engine/utils.py

Line 5 in 0de7156

def _check_signature(fn: Callable, fn_description: str, *args, **kwargs) -> None:

I think this is related to follow_wrapped=True argument of inspect.signature.

Environment

• PyTorch Version (e.g., 1.4): 1.5
• Ignite Version (e.g., 0.3.0): 0.4
• OS (e.g., Linux): MacOS
• How you installed Ignite (conda, pip, source): Honda
• Python version: 3.7
• Any other relevant information: