Static Variables in Python

Python Class Static Variable

• A variable defined inside a class but outside the method is called a static variable.

Example : 

 #program to static variable

 class Team :
     team_name = "INDIA"                # team_name is a static variable
     No_of_players = 11                 # No_of_players is a static variable

     def display_team_member(self,player_list):
         for name in player_list :
             print(name)
         print()
    

• They get memory at class loading time.

• As class load once, so static variable(s) get memory once.

• We can use class name to call static variable, without creating an object.

Example : 

 #program to define class

 class Team :
     team_name = "INDIA"
     No_of_players = 11

     def display_team_member(self,player_list):
         for name in player_list :
             print(name)
         print()

 print("Team_Name", Team.team_name)            # calling by class name without creating Object
 print("No of player : ", Team.No_of_players)  # this call proves that static variable gets memory at class loading time

 #Output

 Team_Name INDIA
 No of player :  11

• They hold common values for every Object.

Example : 

 #program

 class Team :
     team_name = "INDIA"
     No_of_players = 11

     def display_team_member(self,player_list):
         for name in player_list :
             print(name)
         print()

 print("Team_Name", Team.team_name)
 print("No of playesr : ", Team.No_of_players)

 ODI = Team()
 print("\nODI Team_Name", ODI.team_name)
 print("No of playesrs in ODI : ", ODI.No_of_players)

 TEST = Team()
 print("\nTEST Team_Name", TEST.team_name)
 print("No of playesrs in TEST : ", TEST.No_of_players)

 #output

 Team_Name INDIA
 No of playesr :  11

 ODI Team_Name INDIA
 No of playesrs in ODI :  11

 TEST Team_Name INDIA
 No of playesrs in TEST :  11

• If we change the value of a static variable,
• by class

Example:

 #program 

 class Team :
     team_name = "INDIA-A"
     No_of_players = 11

     def display_team_member(self,player_list):
         for name in player_list :
             print(name)
         print()

 print("Team_Name", Team.team_name)
 print("No of player : ", Team.No_of_players)

 ODI = Team()
 print("\nODI Team_Name", ODI.team_name)
 print("No of players in ODI : ", ODI.No_of_players)

 TEST = Team()
 print("\nTEST Team_Name", TEST.team_name)
 print("No of players in TEST : ", TEST.No_of_players)

 Team.team_name = "INDIA-B"       # changing team name by Class name

 print("Team_Name", Team.team_name)
 print("No of player : ", Team.No_of_players)

 print("\nODI Team_Name", ODI.team_name)
 print("No of players in ODI : ", ODI.No_of_players)

 print("\nTEST Team_Name", TEST.team_name)
 print("No of players in TEST : ", TEST.No_of_players)

 #output

 Team_Name INDIA-A
 No of player :  11

 ODI Team_Name INDIA-A
 No of players in ODI :  11

 TEST Team_Name INDIA-A
 No of players in TEST :  11
 Team_Name INDIA-B
 No of player :  11

 ODI Team_Name INDIA-B
 No of players in ODI :  11

 TEST Team_Name INDIA-B
 No of players in TEST :  11

it will change for all the objects of the class.

• by Object

Example : 

 #program

 class Team :
     team_name = "INDIA-A"
     No_of_players = 11

     def display_team_member(self,player_list):
         for name in player_list :
             print(name)
         print()

 print("Team_Name", Team.team_name)
 print("No of players : ", Team.No_of_players)

 ODI = Team()
 print("\nODI Team_Name", ODI.team_name)
 print("No of players in ODI : ", ODI.No_of_players)

 TEST = Team()
 print("\nTEST Team_Name", TEST.team_name)
 print("No of players in TEST : ", TEST.No_of_players)

 ODI.team_name = "INDIA-B"       # changing team name by object ODI

 print("Team_Name", Team.team_name)
 print("No of players : ", Team.No_of_players)

 print("\nODI Team_Name", ODI.team_name)
 print("No of players  in ODI : ", ODI.No_of_players)

 print("\nTEST Team_Name", TEST.team_name)
 print("No of players in TEST : ", TEST.No_of_players)

 #output

 Team_Name INDIA-A
 No of player :  11

 ODI Team_Name INDIA-A
 No of player in ODI :  11

 TEST Team_Name INDIA-A
 No of player in TEST :  11
 Team_Name INDIA-A
 No of player :  11

 ODI Team_Name INDIA-B
 No of player in ODI :  11

 TEST Team_Name INDIA-A
 No of player in TEST :  11

it will be changed for the specific object only, for rest of the objects, value will remain unchanged.