python apply a function after checking if variable is single list or list of lists

Question

I intend to apply a function to a variable. I do not know beforehand if the incoming variable will be a list of list or a single list. e.g

var_name = [a, b, c]
or
var_name = [[a,b,c], [d,e,f], [h,i,j]]

The list of list could contain as many lists as possible. How do I go about verifying if the variable is a list or list of lists. I intend to apply a function depending on the type. I tried to use len(var_name) but the length for list will be the number of items in single list while for list of lists, it is the number of lists in the list of lists.

what I am trying to achieve is this:

#function for list
def apply_val(lst):
    do something with single list
#function for list of list
def apply_val2(lst):
    do something with list of lists

var_name = single_list or list_of_lists
if var_name == single list
    apply_val(single_list)
else:
    apply_val(list_of_lists)

How do I check if the var_name is a list or list of lists?

Answer 1

list of lists does not mean anything, what is [["foo", "bar"], "baz"] ?

However, if you are sure you could only have "list of something that is not a list" and "list of list", just:

• Check the list is not empty
• Then, check the type of first item

if len(my_list) > 0:
  if isinstance(my_list[0], list):
    # List of list
    pass
  else:
    # Simple list
    pass

Answer 2

if the single list is always just values AND the list of lists always contains ONLY lists, you can check if it is a single list or list of lists like so:

list1 = [1,2,3]
list2 = [[1,2,3],[1,2,3]]

if type(list2[0]) == list:
    print('list of lists')
else:
    print('single list')

returns 'list of lists' for list2 and 'single list' for list1

if there is a mix you could do something like:

list3 = [1,[1,2,3], 4.343, 'string']
types = set([type(element) for element in list3])
if list in types and len(types) > 1:
    print('mixed')

Answer 3

Try this

def check_list(test_list):
    if type(test_list[0]) == list:
        return True
    else:
        return False