Python's Dictionary {}

The Python dictionary belongs to a data type, and we can store the data in a dictionary, which is defined using curly braces "{}".
For example, now to store a person's information and then read it, you can use a slice of the way to reflect:

In [1]: info =‘Tom 180 Male‘In [2]: info[1:3]Out[2]: ‘om‘In [3]: info[0:3]Out[3]: ‘Tom‘

So what if we want to save a lot of people's information?

Perhaps we can put the information individually in a single list, and then merge them, but in a way that is very cumbersome in the case of large amounts of data, as shown below:

In [4]: list1=[‘name‘,‘age‘]In [5]: list2=[‘tom‘,‘20‘]In [6]: list3=[‘mike‘,‘24‘]In [7]: zip(list1,list2)Out[7]: [(‘name‘, ‘tom‘), (‘age‘, ‘20‘)]In [8]: list1Out[8]: [‘name‘, ‘age‘]In [9]: list2Out[9]: [‘tom‘, ‘20‘]In [10]: zip(list1,list3)Out[10]: [(‘name‘, ‘mike‘), (‘age‘, ‘24‘)]

A dictionary is the only mapping type (hash table) in Python whose objects are mutable, but the keys of the dictionary must use immutable objects, and a dictionary can use different types of key values, as follows:
Keys ()
VALUES ()
Items ();

First we can create an empty dictionary:

In [11]: dict={}In [12]: type(dict)Out[12]: dict

Define the data as follows:

In [13]: dict={‘a‘:1,1:123}In [14]: dictOut[14]: {1: 123, ‘a‘: 1}                #顺序是可变的，因为遵循哈希表

The data type that is stored in the dictionary should be read-only and the result of the hash should remain the same:

In [15]: dict1={‘a‘:1, 1:123, (‘qq‘,‘wx‘):‘hello‘}In [16]: dict1Out[16]: {1: 123, ‘a‘: 1, (‘qq‘, ‘wx‘): ‘hello‘}

Looking at the length of the dictionary, you can see that the dictionary we just defined has 3 elements:

In [17]: len(dict1)Out[17]: 3

Using the TAB key in Ipython we can see how many ways the dictionary has

In [18]: dict.dict.clear       dict.has_key     dict.itervalues  dict.setdefault  dict.viewkeysdict.copy        dict.items       dict.keys        dict.update      dict.viewvaluesdict.fromkeys    dict.iteritems   dict.pop         dict.values      dict.get         dict.iterkeys    dict.popitem     dict.viewitems   

To view all keys values:

In [18]: dict1.keys()Out[18]: [‘a‘, 1, (‘qq‘, ‘wx‘)]

By looking at all values, you will also return a list of all values stored in the dictionary:

In [19]: dict1.values()Out[19]: [1, 123, ‘hello‘]

Use the keys value to find values:

In [16]: dict1Out[16]: {1: 123, ‘a‘: 1, (‘qq‘, ‘wx‘): ‘hello‘}In [22]: dict1.get(1)Out[22]: 123

If the keys value is not in the dictionary being taken, the value is not returned, but given the keys,values, the values are returned:

In [24]: dict1.get(‘b‘)In [25]: dict1.get(‘b‘,‘c‘)Out[25]: ‘c‘

Determine if keys exist in the dictionary:

In [26]: ‘v‘ in dict1Out[26]: FalseIn [27]: ‘a‘ in dict1Out[27]: True

Or it can be judged as:

In [28]: dict1.has_key(‘v‘)Out[28]: FalseIn [29]: dict1.has_key(‘a‘)Out[29]: True

You can use items to return a dictionary as a list, and then you can iterate over it, or slice it, and get the result you want:

In [16]: dict1Out[16]: {1: 123, ‘a‘: 1, (‘qq‘, ‘wx‘): ‘hello‘}In [30]: dict1.items()Out[30]: [(‘a‘, 1), (1, 123), ((‘qq‘, ‘wx‘), ‘hello‘)]

Update the contents of the dictionary, or update the two dictionaries into a dictionary:

In [35]: dict1Out[35]: {1: 123, ‘a‘: 1, (‘qq‘, ‘wx‘): ‘hello‘}In [36]: dict2Out[36]: {‘e‘: 3, ‘q‘: 1, ‘w‘: 2}In [37]: dict.update(dict1,**dict2)In [38]: dictOut[38]: {1: 123, ‘a‘: 1, ‘e‘: 3, ‘q‘: 1, ‘w‘: 2, (‘qq‘, ‘wx‘): ‘hello‘}

Use the For loop to output the dictionary keys and values:

In [47]: for k in dict1:   ....:     print k,dict1[k]   ....:     a 11 123(‘qq‘, ‘wx‘) hello

Or use items to have the dictionary return a list, and for loop:

In [50]: dict1.items()Out[50]: [(‘a‘, 1), (1, 123), ((‘qq‘, ‘wx‘), ‘hello‘)]In [51]: for k, v in dict1.items(): print k,va 11 123(‘qq‘, ‘wx‘) hello

Dictionary Exercises

#!/usr/local/python3/bin/pythoninfo={}name=input("Please input a number : ")age=input("Please input your age : ")sex=input("Please input your sex(M/F) : ")info[‘name‘]=name  #下标为name的存到info字典里面info[‘age‘]=ageinfo[‘sex‘]=sex#print(info)#print(info.items())for i,w in info.items():    print(‘%s : %s‘ % (i,w))

The operating conditions are as follows:

Please input a number : zyyPlease input your age : 21Please input your sex(M/F) : Fname : zyyage : 21sex : F

Python's Dictionary {}