Common methods of dictionary and traversal in Python

Preface ：

The dictionary is based on “ key — value ” For stored unordered data sets .“ key — value ” Yes, it's a dictionary element , Access the elements in it with “ key ” To visit . The key of the dictionary can be a string 、 Integers 、 Tuple or dictionary . The value of the dictionary can also be a string 、 Integers .

The list cannot be used as a key to the dictionary , Because the list is variable . In the same dictionary , The same key only appears once , It is an index to access other data . If you assign a key repeatedly , The later assigned value will overwrite the previous value . The list can be used as the value of the dictionary .

Common dictionary methods ：

x.keys(),x.values(),x.items() All need parentheses , The three are used in very similar ways , Let's talk about it below x.keys() Mainly .

The return result is ：

dict_keys([' Zhang San ', ' Zhao si ', ' Li Gang ', ' Wang Wu ', ' Wu Liu ', ' Qian Qi '])
<built-in method keys of dict object at 0x0000013DC56A7BD0>

although x.keys Can run successfully , But this is not what we want .

use x.keys(),x.values(),x.items() Method to get the elements in the dictionary , The types returned by these three methods are ：

dict_keys

dict_values

dcit_items

All three types can be converted into list types , Its members can then be accessed by index or slice .

Use list() Just convert it to list type

[' Zhang San ', ' Zhao si ', ' Li Gang ', ' Wang Wu ', ' Wu Liu ', ' Qian Qi ']
however , If you think this traversal is too troublesome , The following methods can be used （ The steps of converting data types are omitted ）.

Next, let's look at an example ：

example ： A dictionary stores a person's name and several city names that the person likes , Go through the dictionary , Print the city everyone likes in the dictionary .

The dictionary is as follows ：

The results to be displayed are as follows ：

Zhao Yi's favorite cities are ： Beijing , Shanghai
Qian Er's favorite cities are ： Hangzhou , ningbo , Xi'an
Sun San's favorite cities are ： shaoxing , changchun
Li Si's favorite cities are ： Beijing
Favorite cities on Friday are ： ningbo , Xi'an , urumqi
Wu Liu's favorite cities are ： urumqi

The code is as follows ：

analysis ： First a It's a dictionary , Where the value is a list , So we need to find the key first , Then traverse the value corresponding to the key （ list ） Content , One by one . We need two for loop , The key to traverse the dictionary for the first time , Traverse the contents of the list for the second time . In the code a[k][i] This function is realized .

If it's too much trouble , You can change the code to use format（） function

in addition ：

Here are x.keys(),x.values(),x.items() Some of the code for , If necessary, you can use

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