python Python字典创建错误
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Python dictionary creation error
提问by Azim
I am trying to create a Python dictionary from a stored list. This first method works
我正在尝试从存储的列表中创建一个 Python 字典。第一种方法有效
>>> myList = []
>>> myList.append('Prop1')
>>> myList.append('Prop2')
>>> myDict = dict([myList])
However, the following method does not work
但是下面的方法不起作用
>>> myList2 = ['Prop1','Prop2','Prop3','Prop4']
>>> myDict2 = dict([myList2])
ValueError: dictionary update sequence element #0 has length 3; 2 is required
So I am wondering why the first method using append works but the second method doesn't work? Is there a difference between myListand myList2?
所以我想知道为什么使用 append 的第一种方法有效，但第二种方法不起作用？有没有之间的差异myList和myList2？
Edit
编辑
Checked again myList2actually has more than two elements. Updated second example to reflect this.
再查一查myList2居然有两个以上的要素。更新了第二个示例以反映这一点。
回答by Daniel Pryden
You're doing it wrong.
你这样做是错的。
The dict()constructor doesn't take a list of items (much less a list containing a single list of items), it takes an iterable of 2-element iterables. So if you changed your code to be:
该dict()构造并不需要的项目的列表（更不用说包含的项目的单列表的列表），它需要一个可迭代2元件iterables的。因此，如果您将代码更改为：
myList = []
myList.append(["mykey1", "myvalue1"])
myList.append(["mykey2", "myvalue2"])
myDict = dict(myList)
Then you would get what you expect:
然后你会得到你所期望的：
>>> myDict
{'mykey2': 'myvalue2', 'mykey1': 'myvalue1'}
The reason that this works:
这样做的原因：
myDict = dict([['prop1', 'prop2']])
{'prop1': 'prop2'}
Is because it's interpreting it as a list which contains one element which is a list which contains two elements.
是因为它将它解释为一个包含一个元素的列表，该列表包含两个元素。
Essentially, the dictconstructor takes its first argument and executes code similar to this:
本质上，dict构造函数接受它的第一个参数并执行类似于以下的代码：
for key, value in myList:
print key, "=", value
