class defaultdict(dict):

    """

    defaultdict(default_factory[, ...]) --> dict with default factory

    The default factory is called without arguments to produce

    a new value when a key is not present, in __getitem__ only.

    A defaultdict compares equal to a dict with the same items.

    All remaining arguments are treated the same as if they were

    passed to the dict constructor, including keyword arguments.

    """

__author__ = 'blackmatrix'

def factory_func():

    return 'default_factory'

test_defaultdict = defaultdict(factory_func)

if __name__ == '__main__':

    '''

    当key存在时，返回的是key对应的value

    这个时候和普通的dict没有什么区别

    '''

    test_defaultdict['a'] = ''

    print(test_defaultdict['a'])

    '''

    当访问不存在的key时，自动将工厂函数的返回值作为默认值

    '''

    print(test_defaultdict['b'])

    print(test_defaultdict['c'])

233333

default_factory

default_factory

from collections import defaultdict

test_defaultdict2 = defaultdict()

print(test_defaultdict2['x'])

# KeyError: 'x'