标签：type ppi 异常 计数器 ons error set 默认 扩展
collections模块提供了一些python内置数据类型的扩展，比如OrderedDict，defaultdict，namedtuple，deque，counter等，简单实用，非常值得学习了解。
import collections顾名思义，有顺序的词典，次序不再是随机的。普通的dict不记录插入的顺序，遍历其值的时候是随机的，相反，OrderedDict记录插入的顺序，在迭代的时候可以看出差异。
print ‘Regular dictionary:‘ d = {} d[‘a‘] = ‘A‘ d[‘b‘] = ‘B‘ d[‘c‘] = ‘C‘ for key, value in d.items(): print key, value Regular dictionary: a A c C b B print ‘OrderedDict:‘ d = collections.OrderedDict() d[‘a‘] = ‘A‘ d[‘b‘] = ‘B‘ d[‘c‘] = ‘C‘ for key, value in d.items(): print key, value OrderedDict: a A b B c C
比较两个词典是否相等，普通词典比较只看内容，内容相同即判定相等为真；而OrderedDict同时会考虑顺序，item被添加的顺序。
print ‘dict :‘, d1 = {} d1[‘a‘] = ‘A‘ d1[‘b‘] = ‘B‘ d1[‘c‘] = ‘C‘ d2 = {} d2[‘b‘] = ‘B‘ d2[‘a‘] = ‘A‘ d2[‘c‘] = ‘C‘ print d1 == d2 dict : True print ‘OrderedDict:‘, d1 = collections.OrderedDict() d1[‘a‘] = ‘A‘ d1[‘b‘] = ‘B‘ d1[‘c‘] = ‘C‘ d2 = collections.OrderedDict() d2[‘b‘] = ‘B‘ d2[‘a‘] = ‘A‘ d2[‘c‘] = ‘C‘ print d1 == d2 OrderedDict: False
普通词典，当你访问没有的键值时，会抛出异常，用defaultdict，可以预先给定默认值，尤其默认值是需要做累积或聚合操作的时候(比如计数)。defaultdict接受一个参数default_factory，该函数负责返回特定的值，可以自定义，也可以用list(返回[ ]) set(返回set()) 或int(返回0)，直接上例子说的比较清楚。
defaultdict其实是继承dict类后。添加了__missing__(key)方法，用于处理KeyError异常。
def default_factory(): return ‘This is default string value‘ d = collections.defaultdict(default_factory) print d[‘foo‘] This is default string value
这里没有定义d[‘foo‘]，但是可以访问，并返回值。下面看点更厉害的！
把default_factory设定为list可以方便地把一系列键值对group起来。默认会返回空的list，下面例子把相同的键group在一起。
s = [(‘yellow‘, 1), (‘blue‘, 2), (‘yellow‘, 3), (‘blue‘, 4), (‘red‘, 1)] d = collections.defaultdict(list) for k, v in s: d[k].append(v) # simpler and faster than d.setdefault(k, []).append(v) d.items() [(‘blue‘, [2, 4]), (‘red‘, [1]), (‘yellow‘, [1, 3])]
计数的时候特别方便，比如要统计每个键值出现多少次。
s = [(‘yellow‘, 1), (‘blue‘, 2), (‘yellow‘, 3), (‘blue‘, 4), (‘red‘, 1)] d = collections.defaultdict(int) for k, v in s: d[k] += 1 d.items() [(‘blue‘, 2), (‘red‘, 1), (‘yellow‘, 2)] s = ‘mississippi‘ d = collections.defaultdict(int) for k in s: d[k] += 1 d.items() [(‘i‘, 4), (‘p‘, 2), (‘s‘, 4), (‘m‘, 1)]
和list功能类似，但返回set(),剔除了重复元素。
s = [(‘red‘, 1), (‘blue‘, 2), (‘red‘, 3), (‘blue‘, 4), (‘red‘, 1), (‘blue‘, 4)] d = collections.defaultdict(set) for k, v in s: d[k].add(v) d.items() [(‘blue‘, {2, 4}), (‘red‘, {1, 3})]
默认的tuple是用数字做索引的，而namedtuple是可以按名字访问，对fields很多，或者创建和使用场景离得比较远的情况，比较有用。
bob = (‘Bob‘, 30, ‘male‘) print ‘Representation:‘, bob jane = (‘Jane‘, 29, ‘female‘) print ‘\nField by index:‘, jane[0] print ‘\nFields by index:‘ for p in [ bob, jane ]: print ‘%s is a %d year old %s‘ % p Representation: (‘Bob‘, 30, ‘male‘) Field by index: Jane Fields by index: Bob is a 30 year old male Jane is a 29 year old female
由于不同的nametuple不一样，我们要单独定义，同时按name访问(依然可以按数字访问)。
# define namedtuple Person = collections.namedtuple(‘Person‘,‘name age gender‘) print ‘Type of Person:‘, type(Person) bob = Person(name=‘Bob‘, age=30, gender=‘male‘) print ‘\nRepresentation:‘, bob bob = Person(‘Bob‘,30,‘male‘) # also supported print ‘Representation:‘, bob jane = Person(name=‘Jane‘, age=29, gender=‘female‘) print ‘\nField by name:‘, jane.name print ‘Field by name:‘, jane[0] Type of Person: <type ‘type‘> Representation: Person(name=‘Bob‘, age=30, gender=‘male‘) Representation: Person(name=‘Bob‘, age=30, gender=‘male‘) Field by name: Jane Field by name: Jane
即double-ended queue，双向队列，支持任何一侧的add和remove操作。普通的stack和queue是deque的退化形式。
当然，deque依然是sequence，所以一些列表类似的操作也是支持的。
d = collections.deque(‘abcdefg‘) print ‘Deque:‘, d print ‘Length:‘, len(d) print ‘Left end:‘, d[0] print ‘Right end:‘, d[-1] d.remove(‘c‘) print ‘remove(c)‘, d Deque: deque([‘a‘, ‘b‘, ‘c‘, ‘d‘, ‘e‘, ‘f‘, ‘g‘]) Length: 7 Left end: a Right end: g remove(c) deque([‘a‘, ‘b‘, ‘d‘, ‘e‘, ‘f‘, ‘g‘])
往队列push元素
import collections # Add to the right d = collections.deque() d.extend(‘abcdefg‘) # append with elements from the iterable print ‘extend :‘, d d.append(‘h‘) print ‘append :‘, d # Add to the left d = collections.deque() d.extendleft(‘abcdefg‘) print ‘extendleft:‘, d d.appendleft(‘h‘) print ‘appendleft:‘, d extend : deque([‘a‘, ‘b‘, ‘c‘, ‘d‘, ‘e‘, ‘f‘, ‘g‘]) append : deque([‘a‘, ‘b‘, ‘c‘, ‘d‘, ‘e‘, ‘f‘, ‘g‘, ‘h‘]) extendleft: deque([‘g‘, ‘f‘, ‘e‘, ‘d‘, ‘c‘, ‘b‘, ‘a‘]) appendleft: deque([‘h‘, ‘g‘, ‘f‘, ‘e‘, ‘d‘, ‘c‘, ‘b‘, ‘a‘])
从双向队列pop元素。
print ‘From the right:‘ d = collections.deque(‘abcdefg‘) while True: try: print d.pop(), except IndexError: break From the right: g f e d c b a print ‘\nFrom the left:‘ d = collections.deque(‘abcdefg‘) while True: try: print d.popleft(), except IndexError: break From the left: a b c d e f g
计数器，顾名思义。构造器接受以下形式，实现初始化。
print collections.Counter([‘a‘, ‘b‘, ‘c‘, ‘a‘, ‘b‘, ‘b‘]) print collections.Counter({‘a‘:2, ‘b‘:3, ‘c‘:1}) print collections.Counter(a=2, b=3, c=1) Counter({‘b‘: 3, ‘a‘: 2, ‘c‘: 1}) Counter({‘b‘: 3, ‘a‘: 2, ‘c‘: 1}) Counter({‘b‘: 3, ‘a‘: 2, ‘c‘: 1})
c = collections.Counter() print ‘Initial :‘, c c.update(‘abcdaab‘) print ‘Sequence:‘, c c.update({‘a‘:1,‘d‘:5}) # increse not replace print ‘Dict :‘, c # add to a and d Initial : Counter() Sequence: Counter({‘a‘: 3, ‘b‘: 2, ‘c‘: 1, ‘d‘: 1}) Dict : Counter({‘d‘: 6, ‘a‘: 4, ‘b‘: 2, ‘c‘: 1})
访问时候利用和字典一样的API。但对于没有的键，不会抛出异常，而是计数为0。
c = collections.Counter(‘abcdaab‘) for letter in ‘abcde‘: print ‘%s : %d‘ % (letter, c[letter]) a : 3 b : 2 c : 1 d : 1 e : 0
产生包含所有元素的一个迭代器。
c = collections.Counter(‘China‘) c[‘z‘] = 0 print c print list(c.elements()) Counter({‘a‘: 1, ‘C‘: 1, ‘i‘: 1, ‘h‘: 1, ‘n‘: 1, ‘z‘: 0}) [‘a‘, ‘C‘, ‘i‘, ‘h‘, ‘n‘]
返回前n个最常见的。
c = collections.Counter(‘abcdaab‘) c.most_common(2) [(‘a‘, 3), (‘b‘, 2)]
标签：type ppi 异常 计数器 ons error set 默认 扩展
原文地址：http://www.cnblogs.com/sjfgod/p/7747084.html
