在字典上迭代,添加键和值
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09-10-2019 - |
题
我想迭代词典,每次都要修改字典,而不是当前发生的事情,这些词典正在用新值重置旧值。
我当前的代码是:
while True:
grades = { raw_input('Please enter the module ID: '):raw_input('Please enter the grade for the module: ') }
但是,可惜的是,这不会修改列表,而是删除了先前的值。我将如何修改字典?
(另外,当我运行此操作时,它希望我输入键之前的值,为什么会发生这种情况?)
解决方案
在您的示例中,每次使用新的钥匙,价值对都会刷新成绩(字典)。
>>> grades = { 'k':'x'}
>>> grades
{'k': 'x'}
>>> grades = { 'newinput':'newval'}
>>> grades
{'newinput': 'newval'}
>>>
您应该做的是更新密钥,值对的相同dict:
>>> grades = {}
>>> grades['k'] = 'x'
>>> grades['newinput'] = 'newval'
>>> grades
{'k': 'x', 'newinput': 'newval'}
>>>
尝试这个:
>>> 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', '': ''}
>>>
其他提示
grades = {}
while True:
module = raw_input(...)
grade = raw_input(...)
if not grades[module]:
grades[module] = []
grades[module].append(grade)
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'))
您正在重新分配(阅读:替换) grades
在每个迭代中,循环。
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
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