Python标准库--collections模块

collections:容器数据类型

__all__ = ['deque', 'defaultdict', 'namedtuple', 'UserDict', 'UserList',
            'UserString', 'Counter', 'OrderedDict', 'ChainMap']

Counter计数器

print(collections.Counter(['a', 'b', 'a', 'c', 'b', 'b']))
print(collections.Counter({'a': 2, 'b': 3, 'c': 1}))
print(collections.Counter('abbabc'))
print(collections.Counter(a=2, b=3, c=1))

c = collections.Counter()
c.update({'a': 2, 'b': 3})
print(c)

"""
Counter({'b': 3, 'a': 2, 'c': 1})
Counter({'b': 3, 'a': 2, 'c': 1})
Counter({'b': 3, 'a': 2, 'c': 1})
Counter({'b': 3, 'a': 2, 'c': 1})
Counter({'b': 3, 'a': 2})
"""

elements() 返回一个迭代器,生成Counter的所有元素

c = collections.Counter('exareedsassagdsfgs')

c['z'] = 0
print(c)
print(list(c.elements()))

"""
Counter({'s': 5, 'e': 3, 'a': 3, 'd': 2, 'g': 2, 'x': 1, 'r': 1, 'f': 1, 'z': 0})
['e', 'e', 'e', 'x', 'a', 'a', 'a', 'r', 'd', 'd', 's', 's', 's', 's', 's', 'g', 'g', 'f']

"""

most_common(3)出现次数最多的3个字母

for letter, count in c.most_common(3):
    print('%s: %7d' % (letter, count))

"""
s:       5
e:       3
a:       3
"""

c1 = collections.Counter('aabbdddeeee')
c2 = collections.Counter('aaabbbcccddd')

print(c1 + c2)
print(c1 - c2)
print(c1 & c2)
print(c1 | c2)

"""
Counter({'d': 6, 'a': 5, 'b': 5, 'e': 4, 'c': 3})
Counter({'e': 4})
Counter({'d': 3, 'a': 2, 'b': 2})
Counter({'e': 4, 'a': 3, 'b': 3, 'd': 3, 'c': 3})
"""

defaultdict 提前指定默认值

def default_factory():
    return 'default value'

d = collections.defaultdict(default_factory, foo='bar')
print('d:', d)
print('foo =>', d['foo'])
print('bar =>', d['bar'])

"""
d: defaultdict(<function default_factory at 0x0000020D79EF3E18>, {'foo': 'bar'})
foo => bar
bar => default value
"""

deque 双端队列, 支持list的一些操作

d = collections.deque('abcdefg')
print(d)
print(len(d))
print(d[0])
print(d[-1])

d.remove('c')
print(d)

"""
deque(['a', 'b', 'c', 'd', 'e', 'f', 'g'])
7
a
g
deque(['a', 'b', 'd', 'e', 'f', 'g'])
"""

左右添加

d1 = collections.deque()
d1.extend('abcdefg')
print(d1)
d1.append('h')
print(d1)

d2 = collections.deque()
d2.extendleft(range(6))
print(d2)
d2.appendleft(6)
print(d2)

"""
deque(['a', 'b', 'c', 'd', 'e', 'f', 'g'])
deque(['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h'])
deque([5, 4, 3, 2, 1, 0])
deque([6, 5, 4, 3, 2, 1, 0])
"""

取出

d = collections.deque('abcdefg')

print(d.pop())
print(d.popleft())

"""
g
a
"""

旋转

d = collections.deque(range(10))
print(d)

d.rotate(2)
print(d)
d.rotate(-2)
print(d)

"""
deque([0, 1, 2, 3, 4, 5, 6, 7, 8, 9])
deque([8, 9, 0, 1, 2, 3, 4, 5, 6, 7])
deque([0, 1, 2, 3, 4, 5, 6, 7, 8, 9])
"""

namedtuple 命名的元祖, 创建一个类,字段名重复或是关键字会报错,使用rename=True对非法字段名重命名.'_index'

Person = collections.namedtuple('Person', 'name age gender')

print(type(Person))

bob = Person(name='bob', age =30, gender='male')
print(bob)

"""
<class 'type'>
Person(name='bob', age=30, gender='male')
"""

OrderedDict 顺序字典
记录插入的顺序,比较时比较顺序

d1 = collections.OrderedDict()
d1['a'] = 'A'
d1['b'] = 'B'
d1['c'] = 'C'

d2 = collections.OrderedDict()
d2['c'] = 'C'
d2['a'] = 'A'
d2['b'] = 'B'

print(d1 == d2)

"""
False
"""