Python Closures - Bangpypers Lightning Talk 2021-10-22

closures.py

"""Examples to show how Python stores the closure metadata in a decorator.

Know that this information isn't always just attached to a decorator. It could
also be passed around with regular functions, if the conditions match.

That is, if a variable from a higher scope is _referenced_ from a variable in
another scope, which is passed around, then, a __closure__ meta variable is
attached to the object that is passed around, where it has a store of what its
'closure' is.

Tip: Snoop around with dir() and id(), and check the value of __closure__ and
it's cell_contents.
"""

import functools

#{{{ Simple decorator
def decorator_1(func):
    def inner_function(*args, **kwargs):
        return func(*args, **kwargs)
    return inner_function

#}}}

#{{{ Clean decorator
def decorator_2(func):
    @functools.wraps(func)
    def inner_function(*args, **kwargs):
        return func(*args, **kwargs)
    return inner_function
#}}}

#{{{ Decorator with extra variables in wrapper
def decorator_3(func):
    x = "Some variable"
    @functools.wraps(func)
    def inner_function(*args, **kwargs):
        return func(*args, **kwargs)
    return inner_function

#}}}

#{{{ Decorator with exposed non local
def decorator_4(func):
    x = "some variable"
    @functools.wraps(func)
    def inner_function(*args, **kwargs):
        print(x)
        return func(*args, **kwargs)
    return inner_function
#}}}