Python中的defaultdict模块和namedtuple模块的简单入门指南

# http://code.activestate.com/recipes/523034/
try:
  from collections import defaultdict
except:
  class defaultdict(dict):
 
    def __init__(self, default_factory=None, *a, **kw):
      if (default_factory is not None and
        not hasattr(default_factory, '__call__')):
        raise TypeError('first argument must be callable')
      dict.__init__(self, *a, **kw)
      self.default_factory = default_factory
 
    def __getitem__(self, key):
      try:
        return dict.__getitem__(self, key)
      except KeyError:
        return self.__missing__(key)
 
    def __missing__(self, key):
      if self.default_factory is None:
        raise KeyError(key)
      self[key] = value = self.default_factory()
      return value
 
    def __reduce__(self):
      if self.default_factory is None:
        args = tuple()
      else:
        args = self.default_factory,
      return type(self), args, None, None, self.items()
 
    def copy(self):
      return self.__copy__()
 
    def __copy__(self):
      return type(self)(self.default_factory, self)
 
    def __deepcopy__(self, memo):
      import copy
      return type(self)(self.default_factory, copy.deepcopy(self.items()))
 
    def __repr__(self):
      return 'defaultdict(%s, %s)' % (self.default_factory, dict.__repr__(self))

二、namedtuple

namedtuple主要用来产生可以使用名称来访问元素的数据对象，通常用来增强代码的可读性，在访问一些tuple类型的数据时尤其好用。其实，在大部分时候你应该使用namedtuple替代tuple，这样可以让你的代码更容易读懂，更加pythonic。举个例子：

from collections import namedtuple
 
# 变量名和namedtuple中的第一个参数一般保持一致，但也可以不一样
Student = namedtuple('Student', 'id name score')
# 或者 Student = namedtuple('Student', ['id', 'name', 'score'])
 
students = [(1, 'Wu', 90), (2, 'Xing', 89), (3, 'Yuan', 98), (4, 'Wang', 95)]
 
for s in students:
  stu = Student._make(s)
  print stu
 
# Output:
# Student(id=1, name='Wu', score=90)
# Student(id=2, name='Xing', score=89)
# Student(id=3, name='Yuan', score=98)
# Student(id=4, name='Wang', score=95)