python - Find out into how many values a return value will be unpacked -

i have function, , when called, i'd know return value going assigned - when unpacked tuple. so:

a = func()         # n = 1 

vs.

a, b, c = func()   # n = 3 

i want use value of n in func. there must magic inspect or _getframe lets me this. ideas?

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disclaimer (because seems neccessary nowadays): know funky, , bad practice, , shouldn't used in production code. looks i'd expect in perl. i'm not looking different way solve supposed "actual" problem, i'm curious how achive asked above. 1 cool usage of trick be:

one, two, 3 = count() one, two, three, 4 = count() 

with

def count():     n = get_return_count()     if not n:         return     return range(n) 

adapted http://code.activestate.com/recipes/284742-finding-out-the-number-of-values-the-caller-is-exp/:

import inspect import dis  def expecting(offset=0):     """return how many values caller expecting"""     f = inspect.currentframe().f_back.f_back     = f.f_lasti + offset     bytecode = f.f_code.co_code     instruction = ord(bytecode[i])     if instruction == dis.opmap['unpack_sequence']:         return ord(bytecode[i + 1])     elif instruction == dis.opmap['pop_top']:         return 0     else:         return 1  def count():     # offset = 3 bytecodes call op unpack op     return range(expecting(offset=3)) 

or object can detect when unpacked:

class count(object):     def __iter__(self):         # offset = 0 because @ unpack op         return iter(range(expecting(offset=0)))