知识问答

如何创建仅包含一个元素的元组

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问题：如何创建仅包含一个元素的元组
回答 0
回答 1
回答 2

问题：如何创建仅包含一个元素的元组

在下面的示例中，我希望所有元素都是元组，为什么当元组仅包含单个字符串时，它会转换为字符串？

>>> a = [('a'), ('b'), ('c', 'd')]
>>> a
['a', 'b', ('c', 'd')]
>>> 
>>> for elem in a:
...     print type(elem)
... 
<type 'str'>
<type 'str'>
<type 'tuple'>
点击查看英文原文

In the below example I would expect all the elements to be tuples, why is a tuple converted to a string when it only contains a single string?

>>> a = [('a'), ('b'), ('c', 'd')]
>>> a
['a', 'b', ('c', 'd')]
>>> 
>>> for elem in a:
...     print type(elem)
... 
<type 'str'>
<type 'str'>
<type 'tuple'>

回答 0

因为前两个元素不是元组；他们只是字符串。括号不会自动使它们成为元组。您必须在字符串后添加一个逗号，以指示python它应该是一个元组。

>>> type( ('a') )
<type 'str'>

>>> type( ('a',) )
<type 'tuple'>

要修复示例代码，请在此处添加逗号：

>>> a = [('a',), ('b',), ('c', 'd')]

             ^       ^

从Python文档：

一个特殊的问题是包含0或1项的元组的构造：语法有一些额外的怪癖来容纳这些项。空元组由一对空括号组成；一个带有一个项目的元组是通过在值后面加上逗号来构造的（仅将一个值括在括号中是不够的）。难看，但是有效。

如果您确实讨厌尾随的逗号语法，则一种解决方法是将a传递list给该tuple()函数：

x = tuple(['a'])
点击查看英文原文

Because those first two elements aren’t tuples; they’re just strings. The parenthesis don’t automatically make them tuples. You have to add a comma after the string to indicate to python that it should be a tuple.

>>> type( ('a') )
<type 'str'>

>>> type( ('a',) )
<type 'tuple'>

To fix your example code, add commas here:

>>> a = [('a',), ('b',), ('c', 'd')]

             ^       ^

From the Python Docs:

A special problem is the construction of tuples containing 0 or 1 items: the syntax has some extra quirks to accommodate these. Empty tuples are constructed by an empty pair of parentheses; a tuple with one item is constructed by following a value with a comma (it is not sufficient to enclose a single value in parentheses). Ugly, but effective.

If you truly hate the trailing comma syntax, a workaround is to pass a list to the tuple() function:

x = tuple(['a'])

回答 1

您的前两个示例不是元组，它们是字符串。单项元组需要逗号结尾，如下所示：

>>> a = [('a',), ('b',), ('c', 'd')]
>>> a
[('a',), ('b',), ('c', 'd')]
点击查看英文原文

Your first two examples are not tuples, they are strings. Single-item tuples require a trailing comma, as in:

>>> a = [('a',), ('b',), ('c', 'd')]
>>> a
[('a',), ('b',), ('c', 'd')]

回答 2

('a') 不是一个元组，而是一个字符串。

您需要在末尾添加一个逗号，以使其python为tuple：-

>>> a = [('a',), ('b',), ('c', 'd')]
>>> a
[('a',), ('b',), ('c', 'd')]
>>>
点击查看英文原文

('a') is not a tuple, but just a string.

You need to add an extra comma at the end to make python take them as tuple: –

>>> a = [('a',), ('b',), ('c', 'd')]
>>> a
[('a',), ('b',), ('c', 'd')]
>>>