Python Design Patterns - Strategy

The strategy pattern is a type of behavioral pattern. The main goal of strategy pattern is to enable client to choose from different algorithms or procedures to complete the specified task. Different algorithms can be swapped in and out without any complications for the mentioned task.

This pattern can be used to improve flexibility when external resources are accessed.

How to implement the strategy pattern?

The program shown below helps in implementing the strategy pattern.

import types

class StrategyExample:
   def __init__(self, func = None):
      self.name = 'Strategy Example 0'
      if func is not None:
         self.execute = types.MethodType(func, self)

   def execute(self):
      print(self.name)

def execute_replacement1(self): 
   print(self.name + 'from execute 1')

def execute_replacement2(self):
   print(self.name + 'from execute 2')

if __name__ == '__main__':
   strat0 = StrategyExample()
   strat1 = StrategyExample(execute_replacement1)
   strat1.name = 'Strategy Example 1'
   strat2 = StrategyExample(execute_replacement2)
   strat2.name = 'Strategy Example 2'
   strat0.execute()
   strat1.execute()
   strat2.execute()

Output

The above program generates the following output −

Explanation

It provides a list of strategies from the functions, which execute the output. The major focus of this behavior pattern is behavior.