Why python not returns None?

Question

class tree :

    def __init__(self):

        self.val=0
        self.right=None
        self.left=None

def create_tree():

    x=input()

    if x==-1:
        return None

    root=tree()
    root.val=x

    print(root)
    print(root.val)
    print(root.right)
    print(root.left)



    while(True):
        print ("reach1")
        root.left=create_tree()
        root.right=create_tree()
        print("reach2")
        break


    return root

def main():

    root=tree()
    root=create_tree()

main()

Why None is not returned when x==-1 in create_tree() ?

sample output:

2 <__main__.tree object at 0x7f58cbf11128> 2 None None reach1
-1 <__main__.tree object at 0x7f58cbf11208>
-1 None None reach1

Becasue -1 != '-1'

Martin Thoma
– Martin Thoma

2018-05-08 10:25:56 +00:00
Commented May 8, 2018 at 10:25 — Martin Thoma
– Martin Thoma, Commented May 8, 2018 at 10:25

Mihai Alexandru-Ionut · Accepted Answer · 2018-05-08 10:33:06Z

8

Why None is not returned when x==-1 in create_tree() ?

Because input() returns a string from stdin input. input reads a line from input, converts it to a string and returns that.

You can check this using type operator.

type_of = type(x)
>> string

The solution is to compare what you've entered with "-1"

if x == "-1":
    return None

or just use int method.

x = int(input())
if x == -1:
    return None

edited May 8, 2018 at 10:33

answered May 8, 2018 at 10:24

Mihai Alexandru-Ionut

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1 Comment

Sean Francis N. Ballais Over a year ago

@IshaanKalsi, if you find that this answers your question, I encourage you to press the green check mark.

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