[Tutor] __getitem__() and for loops

[Gonçalo Rodrigues]

On Fri, 10 Oct 2003 16:39:46 -0400, you wrote:

>Quick question:
>
>Is a for loop actually calling __getitem__() behind the scenes, and passing in the current index of the range of the for loop?
>

Let us test:

>>> class Test(object):
... 	def __init__(self, n):
... 		self.n = int(n)
... 	def __getitem__(self, i):
... 		if 0 <= i < self.n:
... 			return i
... 		else:
... 			raise IndexError
... 
>>> t = Test(4)
>>> for i in t:
... 	print i
... 
0
1
2
3

So it seems...

Python looks first for __iter__ then tries __getitem__ -- also for
backwards compatibility. Before the iterator protocol (< 2.2) coding a
__getitem__ was the standard way to make classes cooperate with
for-loops.

With my best regards,
G. Rodrigues