Python---dict dictionary

PythonDictionary

A dictionary is another mutable container model and can store any type of object.

Each key value of the dictionary (Key=>value) is split with a colon (:), each pair is separated by a comma (,), and the entire dictionary is enclosed in curly braces ({}) , as shown in the following format:

D = {key1:value1, key2:value2}

The key must be unique, but the value does not have to be.

The value can take any data type, but the key must be immutable, such as a string, a number, or a tuple.

A simple Dictionary instance:

Dict = {' Alice ': ' 2341 ', ' Beth ': ' 9102 ', ' Cecil ': ' 3258 '}

You can also create a dictionary like this:

Dict1 = {' abc ': 456}dict2 = {' abc ': 123, 98.6:37}

dict1={} #建立一个空字典
>>> type (DICT1)
< type ' Dict ' >

Add python dictionary elements: two methods

#第一种  >>> dict1[' a ']=1>>> dict1  {' A ': 1}  #第二种: SetDefault method  >>> Dict1.setdefault (' B ', 2)  2  >>> Dict1  

Delete a Python dictionary

#删除指定键-value pairs  >>> dict1  {' A ': 1, ' B ': 2}  >>> del dict1[' a '] #也可以用pop方法, Dict1.pop (' a ')  >>> dict1  {' B ': 2}  #清空字典  >>> dict1.clear ()  >>> dict1 #字典变为空了  {}  #删除字典对象  >>> del dict1  >>> dict1  Traceback (most recent call last):  

Accessing values in the dictionary

Put the corresponding key into square brackets, as follows:

Dict = {' name ': ' Zara ', ' age ': 7, ' Class ': ' First '}  print ("dict[' name ']:", dict[' name ']) print ("dict[' age ']:", dict [' Age '])

#以上实例输出结果:

Dict[' Name ']:  Zaradict[' age ']:7      

If the data is accessed using a key that is not in the dictionary, the output error is as follows:

#!/usr/bin/python  dict = {' Name ': ' Zara ', ' age ': 7, ' Class ': ' First '}  print ("dict[' Alice '):", dict[' Alice ') The above example output: dict[' Zara ']:traceback (most recent call last):  File "test.py", line 4, in <module>    print "Dict [' Alice ']: ", dict[' Alice '); Keyerror: ' Alice '

Modify Dictionary

The way to add new content to a dictionary is to add a new key/value pair, modify or delete an existing key/value pair as follows:

#!/usr/bin/python  dict = {' Name ': ' Zara ', ' age ': 7, ' Class ': ' First '}  dict[' age '] = 8; # Update existing Entrydict [' School '] = "DPS School"; # ADD new entry    print ("dict[' age ']:", dict[' [age ']) print ("dict[' School ']:", dict[' School ']) above instance output: dict[' aged ']:  8dict[' School ']:  DPS School

Delete a dictionary element

The ability to delete a single element also clears the dictionary, emptying only one operation.

Show Delete a dictionary with the Del command, as in the following example:

#!/usr/bin/python#-*-coding:utf-8-*-dict = {' name ': ' Zara ', ' age ': 7, ' Class ': ' First '}  del dict[' Name '] # Delete key is ' N ' Ame ' entry dict.clear ()     # Empty dictionary all Entries del dict         # Delete dictionary  print ("dict[' age '):", dict[' age ') print ("dict[' School '): ", dict[' School ')" but this throws an exception because the dictionary no longer exists after Del: dict[' age ']:traceback (most recent call last):  File "test.py", line 8, in <module>    print "dict[' age '):", dict[' age '); TypeError: ' Type ' object is unsubscriptable

Properties of Dictionary Keys

A dictionary value can take any Python object without restriction, either as a standard object or as a user-defined one, but not a key.

Two important points to keep in mind:

1) The same key is not allowed to appear two times. When created, if the same key is assigned a value of two times, the latter value is remembered, as in the following example:

#!/usr/bin/python  dict = {' name ': ' Zara ', ' age ': 7, ' name ': ' Manni '}  print ("dict[' name ']:", dict[' name ']) Above instance output: dict[' Name ']:  Manni

2) The key must be immutable, so it can be used as a number, string or tuple, so the list is not, the following example:

#!/usr/bin/python  dict = {[' name ']: ' Zara ', ' Age ': 7}  Print ("dict[' name ']:", dict[' name ']) above instance output: Traceback (most recent):  File "test.py", line 3, <module>    dict = {[' Name ']: ' Zara ', ' Age ': 7}; Typeerror:list Objects is unhashable

Dictionary built-in functions & methods

The Python dictionary contains the following built-in functions: CMP (DICT1, DICT2)   compares two dictionary elements. Len (dict)   calculates the number of dictionary elements, that is, the total number of keys. The STR (dict)  output dictionary is a printable string representation. Type (variable) returns  the type of the variable entered, if the variable is a dictionary. The Python dictionary contains the following built-in methods: Radiansdict.clear () removes all elements in the dictionary radiansdict.copy () returns a dictionary of shallow copy Radiansdict.fromkeys () to create a new dictionary, The key that is the dictionary of the elements in the sequence seq, Val is the initial value of the dictionary for all Keys Radiansdict.get (key, Default=none) returns the value of the specified key, if the value does not return the default value in the dictionary Radiansdict.has_key ( Key) returns Falseradiansdict.items () returns a Dict (key, value) tuple array Radiansdict.keys () in the list if the key returns true in the dictionary. Returns a dictionary with a list all keys Radiansdict.setdefault (key, Default=none) and get () are similar, but if the key does not exist in the dictionary, the key is added and the value is set to Defaultradiansdict.update ( DICT2) Update the key/value pairs of the dictionary dict2 to Dict radiansdict.values () returns all values in the dictionary as a list

　　

Python---dict dictionary