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。
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
这是公认答案的延伸,你应该在文本中寻找所有字符的计数。
# Objective: we will only count for non-empty characters
text = "count a character occurrence"
unique_letters = set(text)
result = dict((x, text.count(x)) for x in unique_letters if x.strip())
print(result)
# {'a': 3, 'c': 6, 'e': 3, 'u': 2, 'n': 2, 't': 2, 'r': 3, 'h': 1, 'o': 2}
其他回答
正则表达式非常有用,如果你想要区分大小写(当然还有regex的所有功能)。
my_string = "Mary had a little lamb"
# simplest solution, using count, is case-sensitive
my_string.count("m") # yields 1
import re
# case-sensitive with regex
len(re.findall("m", my_string))
# three ways to get case insensitivity - all yield 2
len(re.findall("(?i)m", my_string))
len(re.findall("m|M", my_string))
len(re.findall(re.compile("m",re.IGNORECASE), my_string))
请注意,regex版本的运行时间大约是它的十倍,只有当my_string非常长或代码处于深度循环中时,这才可能成为问题。
Str.count (sub[, start[, end]]) 返回子字符串sub在范围[start, end]中不重叠出现的次数。可选参数start和end被解释为片表示法。
>>> sentence = 'Mary had a little lamb'
>>> sentence.count('a')
4
a = "I walked today,"
c=['d','e','f']
count=0
for i in a:
if str(i) in c:
count+=1
print(count)
最简单的方法是一行代码:
'Mary had a little lamb'.count("a")
但是如果你想用这个也可以:
sentence ='Mary had a little lamb'
count=0;
for letter in sentence :
if letter=="a":
count+=1
print (count)
正则表达式?
import re
my_string = "Mary had a little lamb"
len(re.findall("a", my_string))