Python 如何提取变量中的字典单键值对

How to extract dictionary single key-value pair in variables

提问by

I have only a single key-value pair in a dictionary. I want to assign key to one variable and it's value to another variable. I have tried with below ways but I am getting error for same.

我在字典中只有一个键值对。我想将键分配给一个变量，并将其值分配给另一个变量。我尝试过以下方法，但同样出现错误。

>>> d = {"a": 1}

>>> d.items()
[('a', 1)]

>>> (k, v) = d.items()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: need more than 1 value to unpack

>>> (k, v) = list(d.items())
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: need more than 1 value to unpack

I know that we can extract key and value one by one, or by for loop and iteritems(), but isn't there a simple way such that we can assign both in a single statement?

我知道我们可以一个一个地提取键和值，或者通过 for 循环 and iteritems()，但是没有一种简单的方法可以让我们在一个语句中同时分配它们吗？

采纳答案by Martijn Pieters

Add another level, with a tuple (just the comma):

添加另一个级别，带有一个元组（只是逗号）：

(k, v), = d.items()

or with a list:

或使用列表：

[(k, v)] = d.items()

or pick out the first element:

或者选择第一个元素：

k, v = d.items()[0]

The first two have the added advantage that they throw an exception if your dictionary has more than one key, and both work on Python 3 while the latter would have to be spelled as k, v = next(iter(d.items()))to work.

前两个具有额外的优势，如果您的字典有多个键，它们会抛出异常，并且两者都适用于 Python 3，而后者必须拼写为k, v = next(iter(d.items()))才能工作。

Demo:

演示：

>>> d = {'foo': 'bar'}
>>> (k, v), = d.items()
>>> k, v
('foo', 'bar')
>>> [(k, v)] = d.items()
>>> k, v
('foo', 'bar')
>>> k, v = d.items()[0]
>>> k, v
('foo', 'bar')
>>> k, v = next(iter(d.items()))  # Python 2 & 3 compatible
>>> k, v
('foo', 'bar')

回答by Ignacio Vazquez-Abrams

You have a list. You must index the list in order to access the elements.

你有一个清单。您必须索引列表才能访问元素。

(k,v) = d.items()[0]

回答by Farhadix

items()returns a list of tuples so:

items()返回元组列表，因此：

(k,v) = d.items()[0]

回答by falsetru

>>> d = {"a":1}
>>> [(k, v)] = d.items()
>>> k
'a'
>>> v
1

Or using next, iter:

或使用next, iter：

>>> k, v = next(iter(d.items()))
>>> k
'a'
>>> v
1
>>>

回答by its me

d = {"a": 1}

you can do

你可以做

k, v = d.keys()[0], d.values()[0]

d.keys()will actually return list of all keys and d.values()return list of all values, since you have a single key:value pair in dyou will be accessing the first element in list of keys and values

d.keys()实际上将返回所有键的d.values()列表并返回所有值的列表，因为您有一个键：值对，d您将访问键和值列表中的第一个元素

回答by kindall

This is best if you have many items in the dictionary, since it doesn't actually create a list but yields just one key-value pair.

如果字典中有很多项目，这是最好的，因为它实际上并没有创建一个列表，而是只产生一个键值对。

k, v = next(d.iteritems())

Of course, if you have more than one item in the dictionary, there's no way to know which one you'll get out.

当然，如果你的字典里有不止一项，你就没有办法知道你会找出哪一项。

回答by Eduard

In Python 3:

在 Python 3 中：

Short answer:

简短的回答：

[(k, v)] = d.items()

or:

或者：

(k, v) = list(d.items())[0]

or:

或者：

(k, v), = d.items()

Long answer:

长答案：

d.items(), basically (but not actually) gives you a list with a tuple, which has 2 values, that will look like this when printed:

d.items(), 基本上（但实际上不是）为您提供一个包含 2 个值的元组的列表，打印时看起来像这样：

dict_items([('a', 1)])

You can convert it to the actual list by wrapping with list(), which will result in this value:

您可以通过用 包装将其转换为实际列表list()，这将导致此值：

[('a', 1)]

回答by KevinG

If you just want the dictionary key and don't care about the value, note that (key, ), = foo.items()doesn't work. You do need to assign that value to a variable.

如果您只想要字典键而不关心值，请注意这(key, ), = foo.items()不起作用。您确实需要将该值分配给变量。

So you need (key, _), = foo.items()

所以你需要 (key, _), = foo.items()

Illustration in Python 3.7.2:

Python 3.7.2 中的插图：

>>> foo = {'a': 1}
>>> (key, _), = foo.items()
>>> key
'a'
>>> (key, ), = foo.items()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: too many values to unpack (expected 1)

回答by Kamlakar Ravindra Bhopatkar

key = list(foo.keys())[0]
value = foo[key]