Python Learning-dictionaries

A dictionary is another mutable container model and can store any type of object.each key value of the dictionary (key=>value) pairs with a colon (:), each pair is separated by a comma (,), the entire dictionary is included in curly braces ({})Medium:

DIC = {key1:value1, key2:value2}

The key must be unique, but the value does not have to be unique, and the value can take any data type, but the key must be immutable, such as a string, a number, or a tuple.

Ex

Id_name = {001:eric,002:lz,003:sky}

Take out the values in the dictionary:

< Span style= "Font-size:12px;background-color:rgb (255,255,255);" >    id_name[003]                     # Put the corresponding key in square brackets

< Span style= "Font-size:12px;background-color:rgb (255,255,255);" >

is output

< Span style= "Font-size:12px;background-color:rgb (255,255,255);" >

< Span style= "Font-size:12px;background-color:rgb (255,255,255);" > New content is added to the dictionary by adding new key/value pairs, modified and deleted as follows:

< Span style= "Font-size:12px;background-color:rgb (255,255,255);" >

id_name = {"001": "Eric", "002": "LZ", "003": "Sky"} 
 id_name["004"] = "Hugo"             &NB Sp               #增加 
 Print (id_name) 
 id_name["002"] = "acer"       &NBS P                     #修改 
 Print (id_name) 
 
 {' 001 ': ' Eric ', ' 004 ': ' Hugo ', ' 003 ': ' Sky ', ' 002 ': ' LZ '} 
 {' 001 ': ' Eric ', ' 004 ': ' Hugo ', ' 003 ': ' Sky ', ' 002 ': ' Acer '} 
 
 
  

< Span style= "Font-size:12px;background-color:rgb (255,255,255);" > can delete a single element can also empty the dictionary, empty only one operation, show Delete a dictionary with the del command

[] #删除键是 entry for "002". Clear () #清空字典

Features of the dictionary key

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:

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;

Id_name = {"001": "Eric", "002": "LZ", "003": "Sky"}

Id_name[] = id_name[] = (id_name)

{' 002 ': ' LZ ', ' 004 ': ' Hugo ', ' 003 ': ' Sky ', ' 001 ': ' Eric '}

{' 002 ': ' Red ', ' 004 ': ' Hugo ', ' 003 ': ' Sky ', ' 001 ': ' Eric '}

2) The key must be immutable, so it can be used as a number, a string or a tuple, so the list does not work;

The dictionary contains the following built-in functions:

CMP (DIRC1,DIRC2)	Comparison of two dictionary elements
Len (DIRC1)	Computes the number of dictionary elements, that is, the total number of keys
STR (DIRC1)	Output dictionary printable string representation
Type (Valu)	Returns the type of the variable, which is the dictionary that returns the dictionary type

The dictionary contains the following built-in methods:

D.clear ()	Delete all elements in a dictionary
D.copy ()	Returns a shallow copy of a dictionary
D.fromkeys ([seq], "Val")	Creates a new dictionary with the elements in the sequence SEQ as keys, and Val is the initial value for all keys in the dictionary
D.get (Keys,default=none)	Returns the value of the specified key, or returns the default value if the value is not in the dictionary
D.keys ()	Returns all keys in the dictionary as a list
D.items ()	Returns an array of traversed (key, value) tuples as a list
D.setdefault (Key,default=none)	Similar to get, but if the key does not add a key in the dictionary, the value is default
D.update (D2)	Update Dictionary d2 key-value pairs to dictionary D
D.values ()	Returns all values in the dictionary as a list
D.has_key (Key)	If the key returns true in the dictionary, it is not returned in the false,3.0 to cancel the

This article is from the "LE" blog, please be sure to keep this source http://lz001.blog.51cto.com/8294567/1792974

Python Learning-dictionaries