为什么在打印列表时没有出现错误时出现 IndexError: string index out of range？

Question

我收到 2 个函数的错误 其中2个功能几乎相同。 在 1 个函数中，我只是打印，在另一个函数中，我将每个单词分配给列表索引中的临时变量，而不是打印。打印的函数没有错误，但是分配单词而不是打印的函数给出了索引超出范围的错误，为什么？ 请检查下面的 the_magic() 和 the_magic1() 函数：

def the_magic(str1,str2):
    str1 = str1
    str2 =  str2
    str3 = []

    for n in str1.split():
        for m in str2.split():
            if m in n:
                str3.append(n)
    if(len(str3)<1):
        str3 = ' '
    print(str3)
    for i  in range(len(str3)):
        print(str3[i])
    return str3

print(str3[i]) gives no error but ...

def the_magic1(str1,str2):
    str1 = str1
    str2 =  str2
    str3 = []

    for n in str1.split():
        for m in str2.split():
            if m in n:
                str3.append(n)
    if(len(str3)<1):
        str3 = ' '
    print(str3)
    for i  in range(len(str3)):
        temp = str3[i]
        if(temp == str2):
            str3 = str2
        else:
            str3 = str3[-1]
    return str3

temp = str3[i] giving error for the_magic1()
# function call :

a = "_MileyCyrus it wont let me do it twitter keeps saying over twitter capacity or something that bird keeps coming up."
b = 'it'
c = " "
b = b.split()
b = b[-1] 
str4=the_magic(a,b) # no error, returns str3 and  also prints each word
str4=the_magic1(a,b) #it gives error : IndexError: string index out of range

Answer 1

for i  in list(str3):
        temp = i
        if(temp == str2):
            str3 = str2
        else:
            str3 = str3[-1]
    return str3

Answer 2

功能不一样。

# instead of printing you have:
    for i  in range(len(str3)):
        temp = str3[i]
        if(temp == str2):
            str3 = str2
        else:
            str3 = str3[-1]
# in the second function.
# problem is, as soon as first word in str3 - which is not a string
# but this list:
# ['it', 'it', 'twitter', 'twitter', 'capacity']
# so if you loop through the words and as soon as one word
# is identical to what is given by `b` (which is `it` in this example)
# str3 (the list) gets set to "it" (str2, here b).
# and if not, str3 gets set to the last word in the list.
# in both cases str3 is not a list any more.

你应该解释你打算用它来编程什么。

对代码的注释

    str1 = str1
    str2 =  str2
    str3 = []

在 Python 中，字符串总是被复制的，因此在处理字符串时无需担心call by reference 问题。 将其简化为：

    str3 = []

    for n in str1.split():
        for m in str2.split():
            if m in n:
                str3.append(n)

显然，您正在搜索 str1 的单词中的哪些单词包含 str2 中给出的任何单词。 剩下的还是看不懂。