为什么一个额外的无类型 str 正在返回？

Question

Here is my code in Python for returning a string in capitalized:

import math
import os
import random
import re
import sys


def solve(s):
    name = list(s.split())

for i in range(len(name)):
    nparts = name[i].capitalize()
    return print (nparts, end = " ")

if __name__ == '__main__':
    fptr = open(os.environ['OUTPUT_PATH'], 'w')

    s = input()

    result = solve(s)

    fptr.write(result + '\n')

    fptr.close()

When I run only the function then the result is ok, but when I try to write the result in a file then I get the error below:

fptr.write(result + '\n')

TypeError: unsupported operand type(s) for +: 'NoneType' and 'str'

By manually checking I found that when I am storing the result into the result variable it also gets an extra value "None". I have no idea why this is going on. Please help.

Answer 1

Your def solve(s): function doesn't return anything so by default it returns None

Fix it to:

def solve(s):
    name = list(s.split())

    return name

Answer 2

To capitalize each word a sentence:

• split it
• loop on it to capitalize each word
• join them by space

import os

def solve(sentence):
    return " ".join(word.capitalize() for word in sentence.split())

if __name__ == '__main__':
    s = input("Give a sentence: ")
    result = solve(s)
    with open(os.environ['OUTPUT_PATH'], 'w') as fptr:
        fptr.write(result + '\n')

Answer 3

When the programmer does not define functions to return anything, Python function by default return None . This is the thing that is happening in your program.

The function solve does not return anything and so returns None which gets stored in the variable result when the function is called

A change that you can make in your program is to return the name.

def solve(s):
    
    name = list(s.split())
    return name

Also, in your program, a return statement cannot be used within a for block. Moreover, name is not defined in your main program. A tip to fix it would be to change the variable name from name to result in your for loop and place the for block after calling the function:

if __name__ == '__main__':
    fptr = open(os.environ['OUTPUT_PATH'], 'w')

    s = input()

    name = solve(s)
    for i in range(len(name)):
        nparts = name[i].capitalize()
        print (nparts, end = " ")

    fptr.write(name[0] + '\n')

    fptr.close()