为什么单个元素元组被解释为python中的那个元素?

问题描述

谁能解释为什么单元素元组在 Python 中被解释为那个元素?

Could anyone explain why single element tuple is interpreted as that element in Python?

和

他们为什么不将元组 (1,) 打印为 (1)?

Why don't they just print the tuple (1,) as (1)?

请看下面的例子:

>>> (1)
1
>>> ((((1))))
1
>>> print(1,)
1
>>> print((1,))
(1,)

推荐答案

单个元素元组永远不会被视为包含的元素.括号主要用于分组，而不是创建元组；逗号就是这样做的.

A single element tuple is never treated as the contained element. Parentheses are mostly useful for grouping, not for creating tuples; a comma does that.

他们为什么不直接将 (1,) 打印为 (1)?

Why don't they just print (1,) as (1)?

可能是因为打印内置容器类型提供了一种表示形式，可用于通过 重新创建容器对象，例如 eval:

Probably because printing a builtin container type gives a representation that can be used to recreate the container object via , say eval:

__repr__的文档a> 对此提供了一些说明:

The docs for __repr__ provides some clarity on this:

如果可能的话，这应该看起来像一个有效的 Python 表达式可用于重新创建具有相同值的对象

If at all possible, this should look like a valid Python expression that could be used to recreate an object with the same value

回答您的问题，(1) 只是带有分组括号的整数 1.为了通过其表示重新创建单例元组，它必须打印为 (1,) 这是创建元组的有效语法.

Answering your question, (1) is just integer 1 with a grouping parenthesis. In order to recreate the singleton tuple via its representation, it has to be printed as (1,) which is the valid syntax for creating the tuple.

>>> t = '(1,)'
>>> i = '(1)'
>>> eval(t)
(1,) # tuple
>>> eval(i)
1    # int

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