Strategy Pattern¶

It belongs to Behavioral Pattern
Also Known As Policy Pattern
Used to control operations of some objects

Summary

It takes a family of Algos

Encapsulates each one

And make them interchangeable with each other

Algos may vary independently

No more if-elif

Each Algo can be unit tested as well as system tested

Shipping Module¶

Supports FedEx, Postal, UPS
Must be extendable

In [1]:

from abc import ABCMeta, abstractmethod

Interface¶

In [2]:

class IPaymentStrategy(metaclass = ABCMeta):
    @abstractmethod
    def calculate(self, order):
        pass

Payment Methods¶

In [3]:

class FedExStrategy(IPaymentStrategy):
    def calculate(self, order):
        return order + 0.1 * order

In [4]:

class PostalStrategy(IPaymentStrategy):
    def calculate(self, order):
        return order + 0.05 * order

In [5]:

class UPSStrategy(IPaymentStrategy):
    def calculate(self, order):
        return order + 0.12 * order

Unified Payment Calculator¶

In [6]:

class ShippingCost():
    def __init__(self, payment_strategy):
        self._payment_strategy = payment_strategy
        
    def shipping_cost(self, order):
        return self._payment_strategy.calculate(order)

Driver Program¶

In [7]:

payment_strategy = FedExStrategy()
cost_calc = ShippingCost(payment_strategy)

print(cost_calc.shipping_cost(30))

33.0

In [8]:

payment_strategy = PostalStrategy()
cost_calc = ShippingCost(payment_strategy)

print(cost_calc.shipping_cost(30))

31.5

In [9]:

payment_strategy = UPSStrategy()
cost_calc = ShippingCost(payment_strategy)

print(cost_calc.shipping_cost(30))

33.6