python--Dictionary

Dictionary

1. Dictionary creation

? Assignment Creation Dictionary

? Create a dictionary from the factory function

# Assignment Creation Dictionary , Key-value, Key- value pair

# Create a dictionary from the factory function

# Create a dictionary using the fromkeys method of the dictionary , with a default value for all elements ;

# If no default value is specified , the default is none;

# Set the default value for each element to "pay ";

2.characteristics of analytic dictionaries ( compared with tuples and lists )

? dictionaries cannot be indexed and sliced , because the dictionary is an unordered data type ;

? dictionaries do not support duplicates and connections ;

? Dictionary support member operators : Judging the dictionary Key whether the value exists in the dictionary ; in, not in

3, the dictionary additions and deletions to search

Increase

Dictionary name [Key] = value

D.update (A=1, b=2)

D.update ({' A ': 1, ' B ', 2})

D.setdefault (' A ', 1)

* * Highlights : differences between SetDefault and The update method

# add key-value to the dictionary by using the dictionary name [Key]=value ]

# Update method implementation added : Key exists , overwriting value , otherwise , Add

It is more recommended that the following method

# SetDefault Implementation Add :

Key exists , overwriting value values ; otherwise , Add

Change

Dictionary name [Key]=value

D.update ({' A ': 2, ' B ': 3})

D.update (a=2, b=3)

Check

View key value ;

View value values ;

View key-value key value pairs ;

See if key exists ;

Services = {' FTP ': $, ' http ': [80, 8080]}

# View key value

Services.keys ()

Services.viewkeys () # give the key a name

Services.iterkeys ()

# View value Values

# View key-value key value pairs

# See if key exists

# View the value values corresponding to the specified key ;

if key does not exist , do not error ; If there is , return value value .

By deleting

--D.pop (key) deletes the dictionary element for the specified key ;

--D.popitem () randomly deletes the key-value element of the dictionary ;

-Del D[key] delete The dictionary element for the specified key ;

--D.clear () Empty the dictionary element

4. Iterate through the dictionary

# iterates through the dictionary's key and value values by default

# The key value of the dictionary is traversed by default

5. Dictionary Application

application 1: implement case statements through a dictionary

? currently Python does not support case statements ;

? Two ways to implement a case statement :

   ? if...elif...elif...else ...

   ? Dictionary implementation

# If: Elif. Elif. Implement

# Dictionary Implementation case Statement

python--Dictionary