从函数返回包含单个项目的元组
刚刚在 Python 中遇到了这一点奇怪的地方，我想我应该记录它 在这里将其写为一个问题，以防其他人试图使用与我相同的毫无结果的搜索词找到答案。 was
看起来元组解包使得如果您希望迭代返回值，则无法返回长度为 1 的元组。 尽管看起来外表是骗人的。查看答案。
>>> def returns_list_of_one(a):
... return [a]
...
>>> def returns_tuple_of_one(a):
... return (a)
...
>>> def returns_tuple_of_two(a):
... return (a, a)
...
>>> for n in returns_list_of_one(10):
... print n
...
10
>>> for n in returns_tuple_of_two(10):
... print n
...
10
10
>>> for n in returns_tuple_of_one(10):
... print n
...
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: 'int' object is not iterable
>>>
Just came across this little bit of weirdness in Python and thought I'd document it write it as a question here in case anyone else is trying to find an answer with the same fruitless search terms I was
Looks like tuple unpacking makes it so you can't return a tuple of length 1 if you're expecting to iterate over the return value. Although it seems that looks are deceiving. See the answers.
>>> def returns_list_of_one(a):
... return [a]
...
>>> def returns_tuple_of_one(a):
... return (a)
...
>>> def returns_tuple_of_two(a):
... return (a, a)
...
>>> for n in returns_list_of_one(10):
... print n
...
10
>>> for n in returns_tuple_of_two(10):
... print n
...
10
10
>>> for n in returns_tuple_of_one(10):
... print n
...
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: 'int' object is not iterable
>>>
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您需要显式地将其设为元组（请参阅官方 教程）：
You need to explicitly make it a tuple (see the official tutorial):
这不是一个错误，一元组是由
val,或(val,)构造的。在 python 语法中定义元组的是逗号而不是括号。您的函数实际上返回
a本身，这当然是不可迭代的。引用序列和元组文档：
This is not a bug, a one-tuple is constructed by
val,or(val,). It is the comma and not the parentheses that define the tuple in python syntax.Your function is actually returning
aitself, which is of course not iterable.To quote sequence and tuple docs:
(a)不是单个元素元组，它只是一个带括号的表达式。使用(a,)。(a)is not a single element tuple, it's just a parenthesized expression. Use(a,).您可以使用
tuple()内置方法来代替那个丑陋的逗号。Instead of that ugly comma, you can use the
tuple()built-in method.