列表索引必须是整数python嵌套字典 [英] list indices must be integers python nested dictionaries

问题描述

在python 3中，我需要一个函数来从嵌套键动态返回值.

In python 3, I need a function to dynamically return a value from a nested key.

nesteddict = {'a':'a1','b':'b1','c':{'cn':'cn1'}}
print(nesteddict['c']['cn']) #gives cn1

def nestedvalueget(keys):
    print(nesteddict[keys])

nestedvalueget(['n']['cn'])

应如何编写nestedvalue?

How should nestedvalueget be written?

我不确定标题的用词是否正确，但是我不确定如何最好地描述这一点.

I'm not sure the title is properly phrased, but I'm not sure how else to best describe this.

推荐答案

如果要遍历字典，请使用循环:

If you want to traverse dictionaries, use a loop:

def nestedvalueget(*keys):
    ob = nesteddict
    for key in keys:
        ob = ob[key]
    return ob

或使用 functools.reduce() :

from functools import reduce
from operator import getitem

def nestedvalueget(*keys):
    return reduce(getitem, keys, nesteddict)

然后使用以下任一版本:

then use either version as:

nestedvalueget('c', 'cn')

请注意，任何一个版本都采用可变数量的参数，以便让您将0个或多个键用作位置参数.

Note that either version takes a variable number of arguments to let you pas 0 or more keys as positional arguments.

演示:

>>> nesteddict = {'a':'a1','b':'b1','c':{'cn':'cn1'}}
>>> def nestedvalueget(*keys):
...     ob = nesteddict
...     for key in keys:
...         ob = ob[key]
...     return ob
... 
>>> nestedvalueget('c', 'cn')
'cn1'
>>> from functools import reduce
>>> from operator import getitem
>>> def nestedvalueget(*keys):
...     return reduce(getitem, keys, nesteddict)
... 
>>> nestedvalueget('c', 'cn')
'cn1'

并澄清您的错误消息:您将表达式['n']['cn']传递给了函数调用，该函数调用定义了一个带有一个元素(['n'])的列表，然后尝试使用字符串'cn'对其进行索引.列表索引只能是整数:

And to clarify your error message: You passed the expression ['n']['cn'] to your function call, which defines a list with one element (['n']), which you then try to index with 'cn', a string. List indices can only be integers:

>>> ['n']['cn']
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: list indices must be integers, not str
>>> ['n'][0]
'n'

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