[Python3] Dictionary (dictionary)

Overview

Dictionnary (dictionary) is the most commonly used data type of Python, which is identified by the square brackets {}, whose elements correspond to Key-value, key and value are separated by a colon: split open, let's look at a basic dictionary creation example:

Dict = {u"key1": U"value1", u"key2" : U"value2"}

Or create it like this:

Dict = {12:u" Blog Park ", u"cnblog": U" Gubei " }

Built-in functions

The built-in functions commonly used in Python are:

• Len
  Used to count the number of dictionary elements, that is, the total number of keys

• Str
  Output dictionary, which is a printable string output dictionary

• Type
  Returns the type of the variable

Let's take a look at how the above three functions apply to the instance Code of the dictionary:

#-*-coding:utf-8-*-__author__= u'Gubei'if __name__=="__main__":        #Dictionary Basic ExampleDict = {u"Blog Park": U"Cnblog", u"Gubei": U"Python3"}            #calculate the length of a dictionary    Print(Len (dict))#output dictionaries as characters, converting dictionaries to stringsStr_d =Str (dict)Print(str_d)Print(dict)#Judging Type    Print(Type (DICT))#Dictionary type    Print(Type (str_d))#string str type

The results of the implementation are as follows:

2{'Blog Park':'Cnblog','Gubei':'Python3'}{'Blog Park':'Cnblog','Gubei':'Python3'}<class 'Dict'><class 'Str'>

Dictionary methods

In Python, there are a number of methods for dictionary processing, let's look at an example:

• Clear
  Empty dictionary

• Copy
  Copy Dictionary

• Fromkeys
  Creates a new dictionary as a Kye, value is the initial value corresponding to all keys

• Get
  Returns the value of the specified key, or returns the default value if the key does not exist

• Inch
  Evaluates if key exists, returns true, otherwise false

• Items
  Returns a tuple that can be traversed, in the form of (Key,value) elements of a tuple

• Keys
  Returns all keys for the dictionary

• SetDefault
  If key exists, it returns its corresponding value, otherwise the key and default value are inserted into the dictionary and the default value is returned

• Update
  Update dictionary

• Values
  Returns all value values of the dictionary

Let's take a look at the practical application of the above method:

#-*-coding:utf-8-*-__author__= u'Gubei'if __name__=="__main__":    Print(U"Dictionary Method Application Example") Dict_demo= {u"Blog Park": U"Cnblog", u"Gubei": U"Python3"} tup1= [1, 2, 3, 4]            #Copy replication DictionaryDICT_CP =dict_demo.copy ()Print(Dict_demo)Print(DICT_CP)#Fromkeys Creating a dictionaryDict_new = Dict.fromkeys (tup1, U"value")    Print(dict_new)#Get Gets the value of the specified keyvalue1 = Dict_demo.get (u"Blog Park", u"I am the default value") value2= Dict_demo.get (U"Python3", u"I am the default value")    Print(value1)Print(value2)#in, determine if key existsKey = U"Blog Park"RESULT1= keyinchDict_demo result2= keyinchdict_newPrint(RESULT1)Print(RESULT2)#items, returns the dictionary all (key, value) as a tupleItems =Dict_demo.items ()Print(items)#keys returns all keys in the dictionary as a listKeys =Dict_demo.keys ()Print(keys)#SetDefault, if key exists, returns its corresponding value,    #Otherwise, the key and default values are inserted into the dictionary and the default values are returnedSET_RESULT1 = Dict_demo.setdefault (u"Blog Park", u"Setting the value") Set_result2= Dict_demo.setdefault (U"I'm a key ."+ R"I am the value")    Print(SET_RESULT1)Print(SET_RESULT2)Print(Dict_demo)#update, updating the dictionarydict_demo.update (dict_new)Print(Dict_demo)#values, returns all the value in the dictionaryValues =dict_demo.values ()Print(values)

Run the results on your own.

Traverse, modify, delete

Let's take a look at how to iterate, modify, and delete the dictionary.

#-*-coding:utf-8-*-__author__= u'Gubei'if __name__=="__main__":    Print(U"dictionary traversal, modification, and deletion examples") Dict_demo= {u"Blog Park": U"Cnblog", u"Gubei": U"Python3"}            #Traversal Method 1     for(Key, value)inchDict_demo.items ():Print("%s:%s"%(key, value))#Traversal Method 2     forKeyinchDict_demo.keys ():Print("%s:%s"%(Key, Dict_demo[key]))#ModifyDict_demo[u"ebook"] = u"the modified value"    Print(Dict_demo)#Delete the specified element    delDict_demo[u"ebook"]    Print(Dict_demo)#Empty Dictionarydict_demo.clear ()Print(Dict_demo)

Summary

• The value of a dictionary can store any type of Python object, which can be either a standard type or a custom type, but key cannot.

• The key of the dictionary is unique and cannot be repeated

• A dictionary key can be a number, a string, or even a tuple, but you cannot use a list

[Python3] Dictionary (dictionary)