Python count sub lists in nested list

Question

I have created a list ->

a = [[1,2,3],[4,5,6],[7,8,9]]

1) How do I get the count of number of sub-lists in a? Like in this case it is 3

2) I am using iterator tool chain for traversing this list

 for elt in itertools.chain.from_iterable(node):

Is there any way to know if I have traversed a sub list ?

Answer 1

as with any other list:

>>> len(a)
3

pythonic way to count sub-lists in a heterogeneous list would be:

>>> sum(isinstance(i, list) for i in a)
3

your second question is not clear. can you not read your code?

Answer 2

1) len(a) is 3.

Answer 3

The number of sub-lists is

len(a)

Each sublist is an element in the list, so you've got three elements in a, each of them is a list with three elements (which are numbers)

Answer 4

if different types are stored in a list you can could sublists this way:

n=0
for b in a:
    if type(b)==type([]):
        n+=1

addition:

yes, sum(1 for x in a if isinstance(x, list)) is more pythonic

Answer 5

1) sum(1 for x in a if isinstance(x, list))

This assumes that there could be things other than lists in a.

2) No. Delegating to itertools generally means you give up knowing anything about the underlying values.