Python cookbook(数据结构与算法)将名称映射到序列元素中的方法

>>> from collections import namedtuple
>>> Sub=namedtuple('Subscriber',['addr','joined'])
>>> subscriber=Sub('lucy@example.com','2016-8-7')
>>> subscriber
Subscriber(addr='lucy@example.com', joined='2016-8-7')
>>> subscriber.addr
'lucy@example.com'
>>> subscriber.joined
'2016-8-7'

>>> len(subscriber)
2
>>> addr,joined=subscriber
>>> addr
'lucy@example.com'
>>> joined
'2016-8-7'
>>>

def compute_cost(records):
  total = 0.0
  for rec in records:
    total += rec[1] * rec[2]
  return total

# example.py
from collections import namedtuple
Stock = namedtuple('Stock', ['name', 'shares', 'price'])
def compute_cost(records):
  total = 0.0
  for rec in records:
    s = Stock(*rec)
    total += s.shares * s.price
  return total
# Some Data
records = [
  ('GOOG', 100, 490.1),
  ('ACME', 100, 123.45),
  ('IBM', 50, 91.15)
]
print(compute_cost(records))

65912.5

>>> s=Stock('ACMS',100,123.45)
>>> s
Stock(name='ACMS', shares=100, price=123.45)
>>> s.shares=75
Traceback (most recent call last):
 File "<pyshell#2>", line 1, in <module>
  s.shares=75
AttributeError: can't set attribute
>>>

>>> s=s._replace(shares=75)
>>> s
Stock(name='ACMS', shares=75, price=123.45)
>>>

from collections import namedtuple
Stock = namedtuple('Stock', ['name', 'shares', 'price','date','time'])
#创建一个包含默认值的“原型”元组
stock_prototype=Stock('',0,0.0,None,None)
#创建一个函数实现将字典转化为Stock类型
def dict_to_stock(s):
  return stock_prototype._replace(**s)
a={'name':'ACMS','shares':100,'price':123.45}
print(dict_to_stock(a))
b={'name':'ACMS','shares':100,'price':123.45,'date':'2016-08-08'}
print(dict_to_stock(b))
c={'name':'ACMS','price':123.45}
print(dict_to_stock(c))

Stock(name='ACMS', shares=100, price=123.45, date=None, time=None)
Stock(name='ACMS', shares=100, price=123.45, date='2016-08-08', time=None)
Stock(name='ACMS', shares=0, price=123.45, date=None, time=None)