Why does this code output 2? 'm' is 0 (false) so why doesn't it output 0 as there is the and expression?
s='hello'
print(s.count('m' and 'l'))
Output:
2
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2 Answers
If you print out print('m' and 'l'), you will realize that it will return l.
Python returns False for an empty string, True for anything else.
When you perform Boolean operations on string, the and operation returns the right-most element, and the or operation return the left most element. (Check out Logical Operators on String in Python)
You can play around with more complex examples:
s='helllmmko'
print(s.count('k' and 'm' and 'l')) # prints count of 'l'
print(s.count('k' or 'm' or 'l')) # prints count of 'k'
print(s.count('k' and 'm' or 'l')) # prints count of 'm'
2 Comments
george salib
so when there is no "m" in "hello" python returns true value (as it's not empty string), I thought it would be equal zero as there is no "m" in "hello" so it count zeroand boolean value would be false?
user12758604
Hey sorry I missed your response. If that's what you want, then it should've been
s.count('m') and s.count('l'). But do note that if both 'm' and 'l' exist in variable s, then it will again return the count of the latter, because other non-boolean variables follows the quirk as well (and returns latter, or returns former).The output of the boolean operations between the strings depends on following things:
- Python considers empty strings as having boolean value of ‘false’ and non-empty string as having boolean value of ‘true’.
- For ‘and’ operator if left value is true, then right value is checked and returned. If left value is false, then it is returned
- For ‘or’ operator if left value is true, then it is returned, otherwise if left value is false, then right value is returned.
Reference: https://www.geeksforgeeks.org/g-fact-43-logical-operators-on-string-in-python/
Now to count occurrences of multiple characters in the string - you can do something like below - https://btechgeeks.com/count-occurrences-of-a-single-or-multiple-characters-in-string-and-find-their-index-positions/
# given string
string = "hello"
# given characters list which should be counted
charlist = ['m', 'l']
# traverse the charlist
for char in charlist:
# counting the number of occurences of given character in the string
charcount = string.count(char)
print("count of ", char, "is :", charcount)
Output:
count of m is : 0
count of l is : 2
