Python 迭代字典，添加键和值
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Iterating on a dictionary, adding keys and values
提问by Hypergiant
I would like to iterate on a dictionary, amending the dictionary each time rather than what is currently happening which is resetting the old value with the new one.
我想迭代字典，每次修改字典而不是当前正在发生的事情，即用新值重置旧值。
My current code is:
我目前的代码是：
while True:
grades = { raw_input('Please enter the module ID: '):raw_input('Please enter the grade for the module: ') }
but alas, this doesn't amend the list, but rather removes the previous values. How would I go about amending the dictionary?
但唉，这不会修改列表，而是删除以前的值。我将如何修改字典？
(Also, when I run this, it wants me to input the value BEFORE the key, why does this happen?)
（此外，当我运行它时，它希望我在键之前输入值，为什么会发生这种情况？）
采纳答案by pyfunc
In your example, grades (dictionary) is getting refreshed each time with a new key,value pair.
在您的示例中，成绩（字典）每次都会使用新的键值对进行刷新。
>>> grades = { 'k':'x'}
>>> grades
{'k': 'x'}
>>> grades = { 'newinput':'newval'}
>>> grades
{'newinput': 'newval'}
>>>
What you should have been doing is update the key,value pair for the same dict:
你应该做的是更新同一个字典的键值对：
>>> grades = {}
>>> grades['k'] = 'x'
>>> grades['newinput'] = 'newval'
>>> grades
{'k': 'x', 'newinput': 'newval'}
>>>
Try this:
试试这个：
>>> grades = {}
>>> while True:
... k = raw_input('Please enter the module ID: ')
... val = raw_input('Please enter the grade for the module: ')
... grades[k] = val
...
Please enter the module ID: x
Please enter the grade for the module: 222
Please enter the module ID: y
Please enter the grade for the module: 234
Please enter the module ID: z
Please enter the grade for the module: 456
Please enter the module ID:
Please enter the grade for the module:
Please enter the module ID: Traceback (most recent call last):
File "<stdin>", line 2, in <module>
KeyboardInterrupt
>>>
>>> grades
{'y': '234', 'x': '222', 'z': '456', '': ''}
>>>
回答by Ivo Wetzel
You're reassigning (read: replacing) gradeson each iteration, of the loop.
您在grades循环的每次迭代中重新分配（读取：替换）。
You need to actually set new keys of the dictionary:
您需要实际设置字典的新键：
grades = {}
while True: // some end condition would be great
id = raw_input('Please enter the module ID: ')
grade = raw_input('Please enter the grade for the module: ')
// set the key id to the value of grade
grades[id] = grade
回答by sjr
grades = {}
while True:
module = raw_input(...)
grade = raw_input(...)
if not grades[module]:
grades[module] = []
grades[module].append(grade)
If you're using python 2.5+:
如果您使用的是 python 2.5+：
import collections
grades = collections.defaultdict(list)
while True:
grades[raw_input('enter module')].append(raw_input('enter grade'))
