Question

我想迭代字典，每次修改字典而不是当前正在发生的字典，而是用新的字符重置旧值。

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: ') }

但是，这不会修改列表，而是删除以前的值。我该如何修改字典？

（另外，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？）

Answer 1

在您的示例中，每次使用新的键值组都会刷新成绩（字典）。

>>> grades = { 'k':'x'}
>>> grades
{'k': 'x'}
>>> grades = { 'newinput':'newval'}
>>> grades
{'newinput': 'newval'}
>>>

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'}
>>>

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', '': ''}
>>>

Answer 2

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'))

Answer 3

你在循环的每次迭代中重新分配（读取：替换）grades。

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

迭代字典，添加键和值

3 个答案: