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

In [1]: from collections import defaultdict
 
In [2]: s = [('xiaoming', 99), ('wu', 69), ('zhangsan', 80), ('lisi', 96), ('wu', 100), ('yuan', 98), ('xiaoming', 89)]
 
In [3]: d = defaultdict(list)
 
In [4]: for k, v in s:
  ...:   d[k].append(v)
  ...:  
 
In [5]: d
Out[5]: defaultdict(<type 'list'>, {'lisi': [96], 'xiaoming': [99, 89], 'yuan': [98], 'zhangsan': [80], 'wu': [69, 100]})
 
In [6]: for k, v in d.items():
  ...:   print '%s: %s' % (k, v)
  ...:  
lisi: [96]
xiaoming: [99, 89]
yuan: [98]
zhangsan: [80]
wu: [69, 100]

s = [('xiaoming', 99), ('wu', 69), ('zhangsan', 80), ('lisi', 96), ('wu', 100), ('yuan', 98), ('xiaoming', 89)]
d = {}
 
for k, v in s:
  d.setdefault(k, []).append(v)

def __missing__(self, key):
  # Called by __getitem__ for missing key
  if self.default_factory is None:
    raise KeyError((key,))
  self[key] = value = self.default_factory()
  return value

In [1]: class MyDefaultDict(dict):
  ...:   def __missing__(self, key):
  ...:     self[key] = 'default'
  ...:     return 'default'
  ...:  
 
In [2]: my_default_dict = MyDefaultDict()
 
In [3]: my_default_dict
Out[3]: {}
 
In [4]: print my_default_dict['test']
default
 
In [5]: my_default_dict
Out[5]: {'test': 'default'}

# 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))

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)