python - 迭代字典，添加键和值

Question

我想迭代字典，每次都修改字典，而不是当前正在发生的用新值重置旧值的情况。

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，唉，这并没有修改列表，而是删除了以前的值。我将如何修改字典？

(另外，当我运行它时，它要我在键之前输入值，为什么会这样？)

Answer 1

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'}
>>> 

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', '': ''}
>>>