Add an attribute to the module in which a Python decorator is running

Question

I'd like to write a Python decorator that adds an attribute to the module in which a decorator is running, ie

@procedure
def whatever(arg1, arg2):
    # do things
    return

should add an attribute attr to the module where whatever is found. I've tried writing the decorator procedure (defined in another file) as follows

def procedure(fn):
    global attr
    attr = SomeClass()
    return fn

but attr is added to the module where procedure is defined, not to the module where procedure runs. Is there some other way to do this?

Answer 1

Suppose you want to mark a function, such that some user of the module where it is defined will be able to know that it belongs to some category of functions. You could write a simple decorator like this:

def special(fn):
    globals().setdefault("__specials__", set()).add(fn)
    return fn

Then you can write a module that uses this decorator, like this:

"""Module 'has_specials'"""
def regular():
    return "meh"

@special
def important():
    return "wow!"

@special
def bigshot():
    return "HA"

This can then be used by another module like this:

import has_specials

if hasattr(has_specials, "__specials__"):
    for fn in has_specials.__specials__:
        print("%-20s: %s" % (fn.__name__, fn))

The code above will import the module, and list the special functions:

important           : <function important at 0x000002435FD51488>
bigshot             : <function bigshot at 0x000002435FD51510>