Python for-in loop preceded by a variable

Question

foo = [x for x in bar if x.occupants > 1]

After googling and searching on here, couldn\'t figure out what this does. Maybe I wasn\'t searching

Answer 1

It's a list comprehension

foo will be a filtered list of bar containing the objects with the attribute occupants > 1

bar can be a list, set, dict or any other iterable

Here is an example to clarify

>>> class Bar(object):
...   def __init__(self, occupants):
...     self.occupants = occupants
... 
>>> bar=[Bar(0), Bar(1), Bar(2), Bar(3)]
>>> foo = [x for x in bar if x.occupants > 1]
>>> foo
[<__main__.Bar object at 0xb748516c>, <__main__.Bar object at 0xb748518c>]

So foo has 2 Bar objects, but how do we check which ones they are? Lets add a __repr__ method to Bar so it is more informative

>>> Bar.__repr__=lambda self:"Bar(occupants={0})".format(self.occupants)
>>> foo
[Bar(occupants=2), Bar(occupants=3)]