Python对于范围（len（str））中的i：最后一次迭代不打印

Question

def fun(str):
    for i in range(len(str)):
        print(i)

string = 'abc'

print(fun(string))

print results are

0
1
2
None

if I change

for i in range(len(str)-1):

the last result is still None

Why is this? And how do I stop it?

Answer 1

When you call print(fun('abc')) , you first call fun , which indeed prints 1 , 2 and 3 , once fun completes, you print its return value. Since you didn't explicitly return anything, Python implicitly returns None for you.

To make a long story short - don't call print on fun , just call fun :

string = 'abc'

fun(string) # Here

Answer 2

You are getting 0, 1, 2 from the print statement in fun function while None is getting printed by:

print(fun(string))

Since, by default a python function returns None that's why you are getting it here. You can directly call it without print statement.

fun(string)

Answer 3

this is because you use print(fun(string)) and you have a print statement inside your function. So it executes the print inside your function and another print with no return value from the function so None.