Python counting elements of a list within a list

Question

Say I have the following list:

L=[ [0,1,1,1],[1,0,1,1],[1,1,0,1],[1,1,1,0] ]

I want to write a code will take a list like this one and tell me if the number of '1s' in each individual list is equal to some number x. So if I typed in code(L,3) the return would be "True" because each list within L contains 3 '1s'. But if I entered code(L,2) the return would be "False". I'm new to all programming, so I'm sorry if my question is hard to understand. Any help would be appreciated.

Answer 1

To see if each sublist has 3 1's in it,

all( x.count(1) == 3 for x in L )

Or as a function:

def count_function(lst,number,value=1):
    return all( x.count(value) == number for x in lst )

L=[ [0,1,1,1],[1,0,1,1],[1,1,0,1],[1,1,1,0] ]
print(count_function(L,3)) #True
print(count_function(L,4)) #False
print(count_function(L,1,value=0)) #True

Answer 2

Assuming your lists contain only 1's and 0's, you can count the ones quite easily: sum(sl). You can get the set of unique counts for sub-lists and test that they all have three 1's as follows:

set( sum(sl) for sl in L ) == set([3])

While a little obscure compared to using the all() approach, this method also lets you test that all sub-lists have the same number of ones without having to specify the number:

len(set( sum(sl) for sl in L )) == 1

You can even "assert" that the sub-lists must all have the same number of 1's and discover that number in one operation:

[n] = set( sum(sl) for sl in L )

This assigns the number of 1's in each sub-list to n, but raises a ValueError if the sub-lists don't all have the same number.