Python | Program to count number of lists in a list of lists

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()

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# 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))

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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.

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# 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))

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Output:

3

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

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

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Method #3 : Using isinstance() method

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# 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))

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Output:

3


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