如何计算字符串中字符出现的次数?

如。“a”在“Mary had a little lamb”中出现了4次。


当前回答

a = 'have a nice day'
symbol = 'abcdefghijklmnopqrstuvwxyz'
for key in symbol:
    print(key, a.count(key))

其他回答

你可以使用循环和字典。

def count_letter(text):
    result = {}
    for letter in text:
        if letter not in result:
            result[letter] = 0
        result[letter] += 1
    return result
a = "I walked today,"
c=['d','e','f']
count=0
for i in a:
    if str(i) in c:
        count+=1

print(count)

你可以使用.count():

>>> 'Mary had a little lamb'.count('a')
4

count绝对是计算字符串中字符出现次数的最简洁和有效的方法,但我尝试使用lambda来提出一个解决方案,类似这样:

sentence = 'Mary had a little lamb'
sum(map(lambda x : 1 if 'a' in x else 0, sentence))

这将导致:

4

另外,这样做还有一个好处,如果句子是包含上述相同字符的子字符串列表,那么由于使用了in,这也会给出正确的结果。看看吧:

sentence = ['M', 'ar', 'y', 'had', 'a', 'little', 'l', 'am', 'b']
sum(map(lambda x : 1 if 'a' in x else 0, sentence))

这也导致:

4

当然,这只会在检查单个字符的出现时起作用,例如在这种特殊情况下“a”。

正则表达式?

import re
my_string = "Mary had a little lamb"
len(re.findall("a", my_string))