Searching through a list of tuples

[Peter Otten]

Repton wrote:

> I often find myself storing data in a list of tuples, and I want to ask
> questions like "what is the index of the first tuple whose 3rd element
> is x", or "give me the first tuple whose 2nd element is y".
> 
> I know I can do [elem for elem in lst if elem[3] == x][0] or (elem for
> elem in lst if elem[2] == y).next() but it feels kinda ugly; is there a
> better way?
> 
> (something like lst.index(x, key=..) or lst.find(y, key=..) would be
> nice)

>>> items = [(1, "a", 10), (2, "b", 20), (3, "c", 30)]
>>> class Key(object):
...     def __init__(self, key):
...             self.key = key
...     def __eq__(self, other):
...             return self.key(other)
...
>>> items.index(Key(lambda x: x[2] == 20))
1
>>> items.index(Key(lambda x: x[1] == "c"))
2

A cleaner and probably faster solution would be to subclass list and
override index()/find().

Peter