Python 速成班练习 8-11：请说明 return 语句的工作原理

Question

我正在阅读“Python 速成课程”这本书，我已经完成了一个关于将列表的副本作为参数传递给函数的练习。我解决不了问题，作者提供的解决方案我也不是很清楚。

这是练习文本：
“不变的魔术师：从练习 8-10 开始。使用魔术师姓名列表的副本调用函数 make_great() 。 Because the original list will be unchanged, return the new list and store it in a separate list。对每个列表调用 show_magicians() 以显示您有一个原始名称列表和一个列表，其中每个魔术师的名字都添加了 Great。“

我的问题确实出在突出显示的行上。为什么需要 return 语句？
我的意思是一旦执行下面代码中的 return magicians 语句，实际上会发生什么？

能否请您也向我解释一下我在注释掉 return 语句时遇到的错误：TypeError: 'NoneType' object is not iterable？

def show_magicians(magicians):
    """Print the name of each magician in the list."""
    for magician in magicians:
        print(magician)

def make_great(magicians):
    """Add 'the Great!' to each magician's name."""
    # Build a new list to hold the great musicians.
    great_magicians = []

    # Make each magician great, and add it to great_magicians.
    while magicians:
        magician = magicians.pop()
        great_magician = magician + ' the Great'
        great_magicians.append(great_magician)

   # Add the great magicians back into magicians.
   for great_magician in great_magicians:
       magicians.append(great_magician)

   return magicians

magicians = ['Harry Houdini', 'David Blaine', 'Teller']
show_magicians(magicians)

print("\nGreat magicians:")
great_magicians = make_great(magicians[:])
show_magicians(great_magicians)

print("\nOriginal magicians:")
show_magicians(magicians)

在此先感谢您！

Answer 1

Return 语句是必需的，因为您要存储 make_great 的结果，即魔术师列表。

great_magicians = make_great(magicians[:])

如果您不提供 return 声明，None 将被 return 编辑。所以你不能在 show_magicians.

中遍历 None

# without return statement great_magicians will be None
great_magicians = make_great(magicians[:])
show_magicians(great_magicians)

Answer 2

首先让我解释一下return语句是如何工作的，函数会继续执行直到有return语句。 return 语句用于结束函数的执行，它 return 将值传递给它的调用者，return 语句之后的代码不会被执行。

例如考虑以下代码。

def get_full_name(first_name, last_name):
    """the function takes first_name and last_name as parameter the concatenates both values and returns the full name"""
    return first_name + " " + last_name
    # if there's further code after the return statement it won't execute.

full_name = get_full_name("Ali", "Muhammad") 
# the value returned by get_full_name function will be assigned to full_name variable.

顺便说一句，您的代码看起来不错！可能在

处有缩进

for great_magician in great_magicians:
    magicians.append(great_magician)
    return magicians

您可以在此处查看工作代码：https://colab.research.google.com/drive/1Ie9Nd9jlgKW5JTx_ZQdAkkEwykarDfv_?usp=sharing

Python 速成班练习 8-11：请说明 return 语句的工作原理

Python crash course Exercise 8-11: Please clarify how the return statement works

python

return

function

list

parameter-passing