Python Training Day3 Essays

Collections Class

This class is equivalent to an extension package that contains some extended operations for data types such as dictionaries, lists, tuples, and so on.

1. Counter counter

#计数器可以列出字符串和列表中元素出现的个数, and returned in a dictionary

>>> import collections>>> li=[' A ', ' B ', ' A ', ' C ', ' A ', ' B ', ' d ', ' d ', ' a ']>>> st= ' Asdasdasdasdasda ' >>> li_c=collections. Counter (LI) >>> st_c=collections.  Counter (ST) >>> print li_ccounter ({' A ': 4, ' B ': 2, ' d ': 2, ' C ': 1}) >>> print st_ccounter ({' A ': 6, ' s ': 5, ' d ': 5}) #通过most_comm () method can specify the element that displays the top n bits of occurrences >>> print Li_c.most_common (3) [(' A ', 4), (' B ', 2), (' d ', 2)]

#update () method to add the statistical results of two counters

>>> import collections>>> li_a=[' A ', ' B ', ' A ', ' C ', ' a ']>>> li_b=[' B ', ' C ']>>> Li_a_ Co=collections. Counter (li_a) >>> li_b_co=collections. Counter (li_b) >>> print li_a_cocounter ({' A ': 3, ' C ': 1, ' B ': 1}) >>> print li_b_cocounter ({' C ': 1, ' B ': 1} ) >>> li_a_co.update (li_b_co) >>> print li_a_cocounter ({' A ': 3, ' C ': 2, ' B ': 2})

2. Ordered dictionary

#有序字典的的操作方法和标准字典完全一致, the only difference is that the key in an ordered dictionary can be shown sequentially, because an ordered dictionary is actually a list of keys that are stored on a standard dictionary and managed by a list of key

>>> Import collections>>> ord_dic=collections. Ordereddict () >>> ord_dic={}

3. Default Dictionary

#标准字典中value的值数据类型是需要提前定义的, otherwise it may be problematic to add data directly to value. For example, the following requirements:

There is a value set [11,22,33,44,55,66,77,88,99,90] that holds all values greater than 66 to the first key in the dictionary, and a value less than 66 to the value of the second key.

That is: {' K1 ': greater Than, ' K2 ': Less than 66}

#传统实现方式

li=[11,22,33,44,55,66,77,88,99,90]list_a=[]list_b=[]dic={' K1 ': list_a, ' K2 ': list_b}for i in li:if i > 66:dic[ ' K1 '].append (i) else:dic[' K2 '].append (i) Print dic

#用默认字典方式

Import collections#coding:utf-8li=[11, 33,44,55,66,77,88,99,90] #用默认字典方法提前定义value的数据类型dic = Collections.defaultdict (list) for value in Li:if value>66:dic[' K1 '].append (value) else:dic[' K2 ']. Append (value) print dic

Queue

#队列分为双向队列和单向队列, all queues are process-safe.

Two-way queue is the queue on both sides can be increased or decreased operation, is FIFO mode

One-way queues can increment and decrement operations only one side, so a one-way queue is a stack.

This article from "Thunderbolt Tofu" blog, declined reprint!

Python Training Day3 Essays