I'm trying to count the letter's 'l' and 'o' in the string below. It seems to work if i count one letter, but as soon as i count the next letter 'o' the string does not add to the total count. What am I missing?
s = "hello world"
print s.count('l' and 'o')
Output: 5
You probably mean s.count('l') + s.count('o').
The code you've pasted is equal to s.count('o'): the and operator checks if its first operand (in this case l) is false. If it is false, it returns its first operand (l), but it isn't, so it returns the second operand (o).
>>> True and True
True
>>> True and False
False
>>> False and True
False
>>> True and 'x'
'x'
>>> False and 'x'
False
>>> 'x' and True
True
>>> 'x' and False
False
>>> 'x' and 'y'
'y'
>>> 'l' and 'o'
'o'
>>> s.count('l' and 'o')
2
>>> s.count('o')
2
>>> s.count('l') + s.count('o')
5
count counts non-overlapping matches. See here.Use regular expression:
>>> import re
>>> len(re.findall('[lo]', "hello world"))
5
or map:
>>> sum(map(s.count, ['l','o']))
5
Alternatively, and since you are counting appearances of multiple letters in a given string, use collections.Counter:
>>> from collections import Counter
>>>
>>> s = "hello world"
>>> c = Counter(s)
>>> c["l"] + c["o"]
5
Note that s.count('l' and 'o') that you are currently using would evaluate as s.count('o'):
The expression
x and yfirst evaluatesx: ifxis false, its value is returned; otherwise,yis evaluated and the resulting value is returned.
In other words:
>>> 'l' and 'o'
'o'
s = "hello world"
sum([s.count(x) for x in ['l','o']])
Output: 5
Count all letters in s:
answer = {i: s.count(i) for i in s}
Then sum any keys (letters) from s:
print(answer['l'] + answer['o'])
O(n^2) where n is the strings length, as opposed to the other answer using a Counter...