Given a list of lists, write a Python program to count the number of lists contained within the list of lists.

Examples:

Input :  [[1, 2, 3], [4, 5], [6, 7, 8, 9]]
Output : 3

Input : [[1], ['Bob'], ['Delhi'], ['x', 'y']]
Output : 4

Method #1 : Using len()

# Python3 program to Count number
# of lists in a list of lists

def countList(lst):
	return len(lst)
	
# Driver code
lst = [[1, 2, 3], [4, 5], [6, 7, 8, 9]]
print(countList(lst))

Output:

3

Method #2 : Using type()

Use a for loop and in every iteration to check if the type of the current item is a list or not, and accordingly increment ‘count’ variable. This method has a benefit over approach #1, as it works well for a list of heterogeneous elements.

# Python3 program to Count number
# of lists in a list of lists

def countList(lst):
	count = 0
	for el in lst:
		if type(el)== type([]):
			count+= 1
			
	return count
	
# Driver code
lst = [[1, 2, 3], [4, 5], [6, 7, 8, 9]]
print(countList(lst))

Output:

3

A one-liner alternative approach for the above code is given below:

def countList(lst):
	return sum(type(el)== type([]) for el in lst)

Method #3 : Using isinstance() method

# Python3 program to Count number
# of lists in a list of lists

def countList(lst):
	return sum(isinstance(i, list) for i in lst)
	
# Driver code
lst = [[1, 2, 3], [4, 5], [6, 7, 8, 9]]
print(countList(lst))

Output:

3