在字符串中查找一个空格，并将字符追加到

def append_after_space(string, character):
    for i in range(len(string)):
        if string[i] == ' ':
            string = string[:i+1] + character + string[i+1:]
            break
    return string

# 示例用法
original_string = "Hello world!"
character_to_append = "T"
modified_string = append_after_space(original_string, character_to_append)
print(modified_string)