05替换空格

请实现一个函数，把字符串中的每个空格替换成"%20"。例如输入“We are happy.”，则输出“We%20are%20happy.”。

# -*- coding:utf-8 -*-
"""
其实，Python的字符串是不可变
没有C++那种像字符串的问题，
但这也导致了，必然多出了空间上的消耗。
"""
def replaceSpace(strings):
    return strings.replace(' ', '%20')

def my_replaceSpace(strings):
    result = ''
    for letter in strings:
        if letter == ' ':
            letter = '%20'
        result += letter
    return result

# def replaceSpace2(strings):
#     pieces = strings.split()
#     result = ''
#     for piece in pieces:
#         result += piece + '%20'
#     result -= '%20'  ## 不可行

if __name__ == '__main__':
    assert replaceSpace('124322') == '124322'
    assert replaceSpace('124 322') == '124%20322'
    assert replaceSpace('123  4566 4356') == '123\%20\%204566\%204356'
    assert replaceSpace(' 124322') == '%20124322'
    assert replaceSpace('124322 ') == '124322%20'
    assert replaceSpace('') == ''
    assert replaceSpace('  ') == '124322%20'
    assert replaceSpace('   ') == '\%20\%20\%20'
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