In [2]:
from abc import ABC, abstractmethod
from collections import namedtuple
In [3]:
Customer = namedtuple('Customer', 'name fidelity')
In [4]:
class LineItem:
def __init__(self, product, quantity, price):
self.product = product
self.quantity = quantity
self.price = price
def total(self):
return self.price * self.quantity
In [18]:
class Order: # The Context
def __init__(self, customer, cart, promotion=None):
self.customer = customer
self.cart = list(cart)
self.promotion = promotion
def total(self):
if not hasattr(self,'__total'):
self.__total = sum(item.total() for item in self.cart)
return self.__total
def due(self):
if self.promotion is None:
discount = 0
else:
discount = self.promotion.discount(self)
return self.total() - discount
def __repr__(self):
fmt = '<Order total: {:.2f} due: {:.2f}>'
return fmt.format(self.total(), self.due())
In [6]:
class Promotion(ABC): # the Strategy: an abstract base class
@abstractmethod
def discount(self, order):
"""Return discount as a positive dollar ammount"""
In [9]:
class FidelityPromo(Promotion): # first Concrete Strategy
"""5% discount for customers with 1000 or more fidelity points"""
def discount(self, order):
return order.total() * .05 if order.customer.fidelity >= 1000 else 0
In [53]:
class BulkItemPromo(Promotion): # second Concrete Strategy
"""10% discount for each LineItem with 20 or more units"""
def discount(self, order):
discount = 0
for item in order.cart:
if item.quantity >= 20:
discount += item.total() * .1
return discount
In [11]:
class LargeOrderPromo(Promotion): # third Concrete Strategy
"""7% discount for oders with 10 or more distinct items"""
def discount(self, order):
distinct_items = {item.product for item in order.cart}
if len(distinct_items) >= 10:
return order.total() * .07
return 0
In [14]:
joe = Customer('John Doe', 0)
ann = Customer('Ann Smith', 1100)
cart = [LineItem('banana', 4, .5),
LineItem('apple', 10, 1.5),
LineItem('watermellon', 5, 5.0)]
In [19]:
Order(joe, cart, FidelityPromo())
Out[19]:
In [20]:
Order(ann, cart, FidelityPromo())
Out[20]:
In [27]:
banana_cart = [LineItem(' banana', 30, .5), LineItem(' apple', 10, 1.5)]
In [52]:
Order(joe, banana_cart, BulkItemPromo())
Out[52]:
In [32]:
long_order = [LineItem(str(item_code), 1, 1.0) for item_code in range(10)]
In [35]:
Order(joe, long_order, LargeOrderPromo())
Out[35]:
In [36]:
Order(joe, cart, LargeOrderPromo())
Out[36]:
In [54]:
from collections import namedtuple
In [57]:
class Order: # The Context
def __init__(self, customer, cart, promotion=None):
self.customer = customer
self.cart = list(cart)
self.promotion = promotion
def total(self):
if not hasattr(self,'__total'):
self.__total = sum(item.total() for item in self.cart)
return self.__total
def due(self):
if self.promotion is None:
discount = 0
else:
discount = self.promotion(self)
return self.total() - discount
def __repr__(self):
fmt = '<Order total: {:.2f} due: {:.2f}>'
return fmt.format(self.total(), self.due())
In [79]:
def fidelity_promo(order):
"""5% discount for customers with 1000 or more fidelity points"""
return order.total() * .05 if order.customer.fidelity >= 1000 else 0
In [80]:
def bulk_item_promo(order):
"""10% discount for each LineItem with 20 or more units"""
discount = 0
for item in order.cart:
if item.quantity >= 20:
discount += item.total() * .1
return discount
In [81]:
def large_order_promo(order):
"""7% discount for oders with 10 or more distinct items"""
distinct_items = {item.product for item in order.cart}
if len(distinct_items) >= 10:
return order.total() * .07
return 0
In [82]:
Order(joe, cart, FidelityPromo)
Out[82]:
In [83]:
Order(ann, cart, FidelityPromo)
Out[83]:
In [84]:
Order(joe, banana_cart, BulkItemPromo)
Out[84]:
In [85]:
Order(joe, long_order, LargeOrderPromo)
Out[85]:
In [86]:
Order(joe, cart, LargeOrderPromo)
Out[86]:
In [87]:
promos = [fidelity_promo, bulk_item_promo, large_order_promo]
In [88]:
def best_promo(order):
"""Select best discount available"""
return max(promo(order) for promo in promos)
In [89]:
Order(joe, long_order, best_promo)
Out[89]:
In [90]:
Order(joe, banana_cart, best_promo)
Out[90]:
In [91]:
Order(ann, cart, best_promo)
Out[91]:
In [92]:
promos = [globals()[name] for name in globals()
if name.endswith('_promo')
and name != 'best_promo']
In [94]:
def best_promo(order):
"""Select best discount available"""
return max(promo(order) for promo in promos)
In [96]:
import inspect
In [98]:
promos = [func for name, func in
inspect.getmembers(promotions, inspect.isfunction)]
In [99]:
class MacroCommand:
"""A command that executes a list of commands"""
def __init__(self, commands):
self.commands = list(commands)
def __call__(self):
for command in self.commands:
command()
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