Python中collections模块的基本使用教程

#!/usr/bin/env python# -*- coding:utf-8 -*-# __author__ = 'liao gao xiang'"""保留最后n个元素"""from collections import dequedef search(file, pattern, history=5): previous_lines = deque(maxlen=history) for l in file: if pattern in l:  yield l, previous_lines # 使用yield表达式的生成器函数，将搜索过程的代码和搜索结果的代码解耦 previous_lines.append(l)with open(b'file.txt', mode='r', encoding='utf-8') as f: for line, prevlines in search(f, 'Python', 5): for pline in prevlines:  print(pline, end='') print(line, end='')d = deque()d.append(1)d.append("2")print(len(d))print(d[0], d[1])d.extendleft([0])print(d)d.extend([6, 7, 8])print(d)d2 = deque('12345')print(len(d2))d2.popleft()print(d2)d2.pop()print(d2)# 在队列两端插入或删除元素时间复杂度都是 O(1) ，区别于列表，在列表的开头插入或删除元素的时间复杂度为 O(N)d3 = deque(maxlen=2)d3.append(1)d3.append(2)print(d3)d3.append(3)print(d3)

class deque(object): """ deque([iterable[, maxlen]]) --> deque object  A list-like sequence optimized for data accesses near its endpoints. """ def append(self, *args, **kwargs): # real signature unknown """ Add an element to the right side of the deque. """ pass def appendleft(self, *args, **kwargs): # real signature unknown """ Add an element to the left side of the deque. """ pass def clear(self, *args, **kwargs): # real signature unknown """ Remove all elements from the deque. """ pass def copy(self, *args, **kwargs): # real signature unknown """ Return a shallow copy of a deque. """ pass def count(self, value): # real signature unknown; restored from __doc__ """ D.count(value) -> integer -- return number of occurrences of value """ return 0 def extend(self, *args, **kwargs): # real signature unknown """ Extend the right side of the deque with elements from the iterable """ pass def extendleft(self, *args, **kwargs): # real signature unknown """ Extend the left side of the deque with elements from the iterable """ pass def index(self, value, start=None, stop=None): # real signature unknown; restored from __doc__ """ D.index(value, [start, [stop]]) -> integer -- return first index of value. Raises ValueError if the value is not present. """ return 0 def insert(self, index, p_object): # real signature unknown; restored from __doc__ """ D.insert(index, object) -- insert object before index """ pass def pop(self, *args, **kwargs): # real signature unknown """ Remove and return the rightmost element. """ pass def popleft(self, *args, **kwargs): # real signature unknown """ Remove and return the leftmost element. """ pass def remove(self, value): # real signature unknown; restored from __doc__ """ D.remove(value) -- remove first occurrence of value. """ pass def reverse(self): # real signature unknown; restored from __doc__ """ D.reverse() -- reverse *IN PLACE* """ pass def rotate(self, *args, **kwargs): # real signature unknown """ Rotate the deque n steps to the right (default n=1). If n is negative, rotates left. """ pass

d = {}for key, value in pairs: if key not in d: d[key] = [] d[key].append(value)

d = defaultdict(list)for key, value in pairs: d[key].append(value)

#!/usr/bin/env python# -*- coding:utf-8 -*-# __author__ = 'liao gao xiang'# 字典中的键映射多个值from collections import defaultdictd = defaultdict(list)print(d)d['a'].append([1, 2, 3])d['b'].append(2)d['c'].append(3)print(d)d = defaultdict(set)print(d)d['a'].add(1)d['a'].add(2)d['b'].add(4)print(d)

from collections import namedtuplewebsites = [ ('Sohu', 'http://www.sohu.com/', u'张朝阳'), ('Sina', 'http://www.sina.com.cn/', u'王志东'), ('163', 'http://www.163.com/', u'丁磊')]Website = namedtuple('Website', ['name', 'url', 'founder'])for website in websites: website = Website._make(website) print website# 输出结果:Website(name='Sohu', url='http://www.sohu.com/', founder=u'/u5f20/u671d/u9633')Website(name='Sina', url='http://www.sina.com.cn/', founder=u'/u738b/u5fd7/u4e1c')Website(name='163', url='http://www.163.com/', founder=u'/u4e01/u78ca')

#!/usr/bin/env python# -*- coding:utf-8 -*-# __author__ = 'liao gao xiang'from collections import Counterwords = [ 'look', 'into', 'my', 'eyes', 'look', 'into', 'my', 'eyes', 'the', 'eyes', 'the', 'eyes', 'the', 'eyes', 'not', 'around', 'the', 'eyes', "don't", 'look', 'around', 'the', 'eyes', 'look', 'into', 'my', 'eyes', "you're", 'under']word_counts = Counter(words)# 出现频率最高的三个单词top_three = word_counts.most_common(3)print(top_three)# Outputs [('eyes', 8), ('the', 5), ('look', 4)]print(word_counts['eyes'])morewords = ['why', 'are', 'you', 'not', 'looking', 'in', 'my', 'eyes']# 如果你想手动增加计数，可以简单的用加法：for word in morewords: print(word) word_counts[word] += 1print(word_counts['eyes'])

#!/usr/bin/env python# -*- coding:utf-8 -*-# __author__ = 'liao gao xiang'from collections import OrderedDictd = OrderedDict()d['foo'] = 1d['bar'] = 2d['spam'] = 3d['grok'] = 4# d['bar'] = 22 #对于一个已经存在的键，重复赋值不会改变键的顺序for key in d: print(key, d[key])print(d)import jsonprint(json.dumps(d))

#!/usr/bin/env python# -*- coding:utf-8 -*-# __author__ = 'liao gao xiang'from collections import ChainMapfrom itertools import chain# 不同集合上元素的迭代a = [1, 2, 3, 4]b = ('x', 'y', 'z')c = {1, 'a'}# 方法一，使用chainfor i in chain(a, b, c): print(i)print('--------------')# 方法二，使用chainmapfor j in ChainMap(a, b, c): print(j)# 这两种均为节省内存，效率更高的迭代方式

#!/usr/bin/env python# -*- coding:utf-8 -*-# __author__ = 'liao gao xiang'# 合并多个字典和映射a = {'x': 1, 'z': 3}b = {'y': 2, 'z': 4}# 现在假设你必须在两个字典中执行查找操作# (比如先从 a 中找，如果找不到再在 b 中找)。# 一个非常简单的解决方案就是使用collections模块中的ChainMap类from collections import ChainMapc = ChainMap(a, b)print(c)a['x'] = 11 # 使用ChainMap时，原字典做了更新，这种更新会合并到新的字典中去print(c) # 按顺序合并两个字典print(c['x'])print(c['y'])print(c['z'])# 对于字典的更新或删除操作影响的总是列中的第一个字典。c['z'] = 10c['w'] = 40del c['x']print(a)# del c['y']将出现报错# ChainMap对于编程语言中的作用范围变量（比如globals,locals等）# 是非常有用的。事实上，有一些方法可以使它变得简单：values = ChainMap() # 默认会创建一个空字典print('/t', values)values['x'] = 1values = values.new_child() # 添加一个空字典values['x'] = 2values = values.new_child()values['x'] = 30# values = values.new_child()print(values, values['x']) # values['x']输出最后一次添加的值values = values.parents # 删除上一次添加的字典print(values['x'])values = values.parentsprint(values)a = {'x': 1, 'y': 2}b = {'y': 2, 'z': 3}merge = dict(b)merge.update(a)print(merge['x'], merge['y'], merge['z'])a['x'] = 11print(merge['x'])