[Tutor] list.index() question

[Steven D'Aprano]

Robert Berman wrote:
> Hi,
> 
> Assuming a list similar to this: l1=[['a',1],['b',2],['c',3]] and I want 
> to get the index of 'c'.

You will need to explain what you mean by "the index of 'c'".

Do you mean 0, because 'c' is in position 0 of the sub-list ['c', 3]?

Or do you mean 2, because 'c' is in the sub-list at position 2?

What happens if there is a sub-list ['d', 'c']? Should that also count? What 
about sub-sub-lists, should they be checked too?

Here is a version which checks each sub-list in turn, and returns the index of 
any 'c' it finds of the first such sub-list.

def inner_find(list_of_lists):
     for sublist in list_of_lists:
         try:
             return sublist.index('c')
         except ValueError:
             pass  # go to the next one
     # If not found at all:
     raise ValueError('not found')


Here's a version which finds the index of the first sub-list that begins with 
'c' as the zeroth element:

def match_sublist(list_of_lists):
     for i, sublist in enumerate(list_of_lists):
         if sublist and sublist[0] == 'c':
             return i
     raise ValueError('not found')




Other variations on these two techniques are left for you to experiment with.



-- 
Steven