python更新字典与循环中的字典

Question

I am trying to update a dictionary with an other dictionary in a loop

    mainDict = {}
    for index in range(3):
        tempDict = {}
        tempDict['a'] = 1
        tempDict['b'] = 2
        mainDict.update(tempDict)

Output:

>>> print mainDict
{'a': 1, 'b': 2}

What I am expecting is:

{{'a': 1, 'b': 2},{'a': 1, 'b': 2},{'a': 1, 'b': 2}}    

Any suggestions please. Thanks.

Answer 1

Dictionaries are key-value pairs. In your expected output there is no dictionary. Either you want a list , and in this case use:

main_list = []
for (...)
    main_list.append(temp_dict)

or add keys in the loop:

mainDict = {}
for index in range(3):
    tempDict = {}
    tempDict['a'] = 1
    tempDict['b'] = 2
    mainDict[index] = tempDict

Answer 2

As others commented in the comments section, python dictionaries keys must be unique. Quoting from python docs :

It is best to think of a dictionary as an unordered set of key: value pairs, with the requirement that the keys are unique (within one dictionary)

Possible solution : Create a list instead of a dict to store the dictionaries.