python小程序——统计文件中单词出现的次数

1、统计文件中第一个单词出现的次数

方法一：先把所有不重复的首个单词保存为列表，然后用字典的fromkeys方法把字典初始化为键为首单词值为0的字典，最后再循环一次统计单词出现的次数，该方法的算法复杂度较高，如文件有n行，则为O(n*n)

def count_word():
    count = {}
    keys = []
    with open('test.txt') as f:
        lines = f.readlines()
    for line in lines:
        first_word = line.split(' ')[0]
        if first_word not in keys:
            keys.append(first_word)
    count = count.fromkeys(keys,0) #fromkeys方法不会直接修改原字典，它会返回一个新字典，所以如果要使用心字典必须先赋值
    print(count)
    for line in lines:
        first_word = line.split(' ')[0]
        count[first_word] +=1
    print(count)

方法二：在找到每行的第一个单词时，先用字典的has_key方法确认字典中是否有这个键，如无，则新增键为该单词，值为1的项，如字典已有该项，则该项的值+1，该算法复杂度为O(n)

def count_word():
    count = {}
    with open('test.txt') as f:
        lines = f.readlines()
    for line in lines:
        first_word = line.split(' ')[0]
        if count.has_key(first_word):
            count[first_word] +=1
        else:
            count[first_word] = 1
    print(count)

2、统计一篇文章中某个单词的出现次数
分别用两个for循环即可，for line in lines: for word in line.split(' '):

def count_word():
    mark_word = 'error'
    count = 0
    with open('test.txt') as f:
        lines = f.readlines()
    for line in lines:
        for word in line.split(' '):
            if word == mark_word:
                count +=1
    print(count)