python - 字典键数

Question

在 Python 2.7 中:我正在测量一个对函数返回的字典的键进行计数的过程。

显示了一个基本示例，其中函数 getList() 返回一个字符列表，可能是 ['a']、['b']、['c'] 或 ['d' '];大多数列表都是单个元素，尽管有时可能会返回两个元素，例如['广告']。我想统计所有退回的东西。我想到的一种方法如下所示:

    myDict = {'a':0, 'b':0, 'c':0, 'd':0, 'error':0, 'total':0}
    for key in charList:
        myDict[key] += 1
        myDict['total'] += 1

有没有一种更Pythonic的方式，也许是字典理解来计算列表(不同长度)中的键？

import random

def getList():
    '''mimics a prcoess that returns a list of chars between a - d
       [most lists are single elements, though some are two elements]'''
    number = (random.randint(97,101))
    if number == 101:
        charList = [chr(number-1), chr(random.randint(97,100))]
        if charList[0] == charList[1]:
            getList()            
    else:
        charList = [chr(number)]
    return charList


myDict = {'a':0, 'b':0, 'c':0, 'd':0, 'error':0, 'total':0}

for counter in range(0,5):
    charList = getList()
    for key in charList:
        print charList, '\t', key
        try:
            myDict[key] += 1
            myDict['total'] += 1
        except:
            myDict['error'] += 1

print "\n",myDict

生成的输出:

Answer 1

您可以使用内置的collections.Counter类:https://docs.python.org/2/library/collections.html#collections.Counter

例如您的代码:

import collections
ctr = collections.Counter()

for ii in range(0,5):
    charList = getList()
    ctr.update(charList)

ctr['total'] = sum(ctr.values())
print ctr

这将打印:

Counter({'total': 7, 'd': 5, 'a': 1, 'c': 1})