http://docs.python.org/2/library/itertools.html#itertools.chain.from_iterable

>>> class A:
...   @classmethod
...   def from_iterable(iterables):
...     for it in iterables:
...       for element in it:
...         yield element
... 
>>> A.from_iterable(['ABC', 'DEF'])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: from_iterable() takes 1 positional argument but 2 were given
>>>