Getting callable object from the frame

Question

Given the frame object (as returned by sys._getframe, for instance), can I get the underlying callable object?

Code explanation:

def foo():
    frame = sys._getframe()
    x = some_magic(frame)

    # x is foo, now

Note that my problem is getting the object out of a frame, not the currently called object.

Hope that's possible.

Cheers,

MH

EDIT:

I've somewhat managed to work around this problem. It was heavily inspired by Andreas' and Alexander's replies. Thanks guys for the time invested!

def magic():
    fr = sys._getframe(1)
    for o in gc.get_objects():
        if inspect.isfunction(o) and o.func_code is fr.f_code:
            return o 

class Foo(object):
    def bar(self):
        return magic()

x = Foo().bar()

assert x is Foo.bar.im_func

(works in 2.6.2, for py3k replace func_code with __code__ and im_func with __func__)

Then, I can aggressively traverse globals() or gc.get_objects() and dir() everything in search for the callable with the given function object.

Feels a bit unpythonic for me, but works.

Thanks, again!

MH

Answer 1

To support all cases, including the function being part of a class or just a global function, there is no straight-forward way of doing this. You might be able to get the complete call stack and iterate your way down through globals(), but it wouldn't be nice...

The closest I can get you is this:

import sys, types

def magic():
    # Get the frame before the current one (i.e. frame of caller)
    frame = sys._getframe(1)
    # Default values and closure is lost here (because they belong to the
    # function object.)
    return types.FunctionType(frame.f_code, frame.f_globals)

class MyClass(object):
    def foo(self, bar='Hello World!'):
        print bar
        return magic()

test = MyClass()

new_foo = test.foo()
new_foo(test, 'Good Bye World!')

You'll be executing the exact same code, but it'll be in a new code wrapper (e.g., FunctionType.)

I suspect you want to be able to restore the state of your application based on a stack... Here's something that will at least call the functions as similarly as possible to the original calls (the closure is still left out, because if you could get closures from the frames, getting the function that was called would be pretty easy):

import sys, types

class MyClass(object):
    def __init__(self, temp):
        self.temp = temp

    def foo(self, bar):
        print self.temp, bar
        return sys._getframe()

def test(hello):
    print hello, 'World!'
    return sys._getframe()

def recall(frame):
    code = frame.f_code
    fn = types.FunctionType(
        code, frame.f_globals, code.co_name,
        # This is one BIG assumption that arguments are always last.
        tuple(frame.f_locals.values()[-code.co_argcount:]))
    return fn()


test1 = MyClass('test1')
frame1 = test1.foo('Hello World!')

test2 = MyClass('test2')
frame2 = test2.foo('Good Bye World!')
frame3 = test2.foo('Sayonara!')

frame4 = test('HI')

print '-'

recall(frame4)
recall(frame3)
recall(frame2)
recall(frame1)

Answer 2

A little ugly but here it is:

frame.f_globals[frame.f_code.co_name]

Full example:

#!/usr/bin/env python

import sys

def foo():
  frame = sys._getframe()
  x = frame.f_globals[frame.f_code.co_name]

  print foo is x

foo()

Prints 'True'.

Answer 3

Not really an answer, but a comment. I'd add it as a comment, but I don't have enough "reputation points".

For what it's worth, here's a reasonable (I think) use case for wanting to do this sort of thing.

My app uses gtk, and spins a lot of threads. As anyone whose done both of these at once knows, you can't touch the GUI outside the main thread. A typical workaround is to hand the callable that will touch the GUI to idle_add(), which will run it later, in the main thread, where it is safe. So I have a lot of occurrences of:

def threaded_gui_func(self, arg1, arg2):
    if threading.currentThread().name != 'MainThread':
        gobject.idle_add(self.threaded_gui_func, arg1, arg2)
        return
    # code that touches the GUI

It would be just a bit shorter and easier (and more conducive to cut-n-paste) if I could just do

def thread_gui_func(self, arg1, arg2):
    if idleIfNotMain(): return
    # code that touches the GUI

where idleIfNotMain() just returns False if we are in the main thread, but if not, it uses inspect (or whatever) to figure out the callable and args to hand off to idle_add(), then returns True. Getting the args I can figure out. Getting the callable appears not to be too easy. :-(