Python return occurrence of n lists recursively without slicing / deepcopy or inbuilt functions-CodePudding

You cannot use inbuilt functions or slicing or deepcopy or copy, or while or for

Lets say this is our function:

def list_occur(n):

it takes n as int parameter input and returns a list with size n that shows the element n in this series ( output ):

n = 0: returns []
n = 1: returns list with size 1 that takes in index=0 [], means returns [ [] ]
n = 2: returns list with size 2 that takes in index=0 [] and index = 1 [ [] ], means returns:
[ [], [ [] ] ]
n = 3: returns list with size 3 that takes in index=0 [], index =1 [ [] ], index = 2 [ [], [ [] ] ] 
means its returns [ [], [ [] ], [ [], [ [] ] ] ]

my try to solve this problem, but i get error "AttributeError: 'NoneType' object has no attribute 'append' when i try n = 2 :

  def occur(n) :

    return occr_helper(n)



def occr_helper(n) :

    if (n == 0):
        return []

    return occr_helper(n-1).append(occr_helper(n-1))

    if __name__ == "__main__":

    print(occur(1))

CodePudding user response：

For this function n 1 returns n appended to n. This can easily be coded recursively:

num = 3

def occr(n):
    if n == 0:
        return []
    else:
        new_l = occr(n-1)
        new_l.append(occr(n-1))
        return new_l

print(occr(num))