Python 3 How to check if a value is already in a list in a list

Question

I have a list of lists in my Python 3:

mylist = [[a,x,x][b,x,x][c,x,x]]

(x is just some data)

I have my code which does that:

for sublist in mylist:
    if sublist[0] == a:
        sublist[1] = sublist[1]+1
        break

now I want to add an entry, if there is any sublistentry ==a

How can I do that?

Answer 1

Use any() to test the sublists:

if any(a in subl for subl in mylist):

This tests each subl but exits the generator expression loop early if a match is found.

This does not, however, return the specific sublist that matched. You could use next() with a generator expression to find the first match:

matched = next((subl for subl in mylist if a in subl), None)
if matched is not None:
    matched[1] += 1

where None is a default returned if the generator expression raises a StopIteration exception, or you can omit the default and use exception handling instead:

try:
    matched = next(subl for subl in mylist if a in subl)
    matched[1] += 1
except StopIteration:
    pass # no match found