stackoverflow-answer.md

Ideas proposed here are excellent, but have some disadvantages:

1. inspect.getouterframes and args[0].__class__.__name__ are not suitable for plain functions and static-methods.
2. __get__ must be in a class, that is rejected by @wraps.
3. @wraps itself should be hiding traces better.

So, I've combined some ideas from this page, links, docs and my own head,
and finally found a solution, that lacks all three disadvantages above.

As a result, method_decorator:

• Knows the class the decorated method is bound to.
• Hides decorator traces by answering to system attributes more correctly than functools.wraps() does.
• Is covered with unit-tests for bound an unbound instance-methods, class-methods, static-methods, and plain functions.

Usage:

pip install method_decorator
from method_decorator import method_decorator

class my_decorator(method_decorator):
    # ...

See full unit-tests for usage details.

And here is just the code of the method_decorator class:

class method_decorator(object):

    def __init__(self, func, obj=None, cls=None, method_type='function'):
        # These defaults are OK for plain functions
        # and will be changed by __get__() for methods once a method is dot-referenced.
        self.func, self.obj, self.cls, self.method_type = func, obj, cls, method_type

    def __get__(self, obj=None, cls=None):
        # It is executed when decorated func is referenced as a method: cls.func or obj.func.

        if self.obj == obj and self.cls == cls:
            return self # Use the same instance that is already processed by previous call to this __get__().

        method_type = (
            'staticmethod' if isinstance(self.func, staticmethod) else
            'classmethod' if isinstance(self.func, classmethod) else
            'instancemethod'
            # No branch for plain function - correct method_type for it is already set in __init__() defaults.
        )

        return object.__getattribute__(self, '__class__')( # Use specialized method_decorator (or descendant) instance, don't change current instance attributes - it leads to conflicts.
            self.func.__get__(obj, cls), obj, cls, method_type) # Use bound or unbound method with this underlying func.

    def __call__(self, *args, **kwargs):
        return self.func(*args, **kwargs)

    def __getattribute__(self, attr_name): # Hiding traces of decoration.
        if attr_name in ('__init__', '__get__', '__call__', '__getattribute__', 'func', 'obj', 'cls', 'method_type'): # Our known names. '__class__' is not included because is used only with explicit object.__getattribute__().
            return object.__getattribute__(self, attr_name) # Stopping recursion.
        # All other attr_names, including auto-defined by system in self, are searched in decorated self.func, e.g.: __module__, __class__, __name__, __doc__, im_*, func_*, etc.
        return getattr(self.func, attr_name) # Raises correct AttributeError if name is not found in decorated self.func.

    def __repr__(self): # Special case: __repr__ ignores __getattribute__.
        return self.func.__repr__()