python - "yield from iterable" vs "return iter(iterable)" -

when wrapping (internal) iterator 1 has reroute __iter__ method underlying iterable. consider following example:

class fancynewclass(collections.iterable):     def __init__(self):         self._internal_iterable = [1,2,3,4,5]      # ...      # variant     def __iter__(self):         return iter(self._internal_iterable)      # variant b     def __iter__(self):         yield self._internal_iterable 

is there significant difference between variant , b? variant returns iterator object has been queried via iter() internal iterable. variant b returns generator object returns values internal iterable. 1 or other preferable reason? in collections.abc yield from version used. return iter() variant pattern have used until now.

the significant difference happens when exception raised within iterable. using return iter() fancynewclass not appear on exception traceback, whereas yield from will. thing have information on traceback possible, although there situations want hide wrapper.

other differences:

• return iter has load name iter globals - potentially slow (although unlikely affect performance) , messed (although overwrites globals deserves get).

• with yield from can insert other yield expressions before , after (although equally use itertools.chain).

• as presented, yield from form discards generator return value (i.e. raise stopexception(value). can fix writing instead return (yield iterator).

here's test comparing disassembly of 2 approaches , showing exception tracebacks: http://ideone.com/1yvcse

using return iter():

  3           0 load_global              0 (iter)               3 load_fast                0 (it)               6 call_function            1 (1 positional, 0 keyword pair)               9 return_value traceback (most recent call last):   file "./prog.py", line 12, in test   file "./prog.py", line 10, in runtimeerror 

using return (yield from):

  5           0 load_fast                0 (it)               3 get_iter               4 load_const               0 (none)               7 yield_from               8 return_value traceback (most recent call last):   file "./prog.py", line 12, in test   file "./prog.py", line 5, in bar   file "./prog.py", line 10, in runtimeerror