How to count number of occurrences of a substring inside a string in Python?

Question

I am attempting to write a code snippet that requests from the user to enter a string s and then a substring ss. The program will then have to count the number of occurrences of ss in s. For example if the user enters s = ‘azcbobobegghakl’ and ss = ‘bob’, then the program should print: Number of times bob occurs is: 2.

Here is my code so far :

def count(s,ss):
    Occurrence = 0
    if ss in s :
        for ss in s :
            Occurrence += 1
    return Occurrence 

#Main program : 
    
s = str(input("Choose a string: "))
    
ss = str(input("Choose a substring:")) 
    
print ("Number of times " + str(ss) + " occurs is : " + str(count(s,ss)) )

My desired output would be this:

Choose a string: hellohel
Choose a substring:hel
Number of times hel occurs is : 2

But instead I get this :

Choose a string: hellohel
Choose a substring:hel
Number of times hel occurs is : 8

So can someone please help me modify this code to deliver the desire output? Thanks in advance

Ironkey · Accepted Answer · 2020-10-20T14:30:43.277

3

you can use count

print("hellohel".count("hel"))

If you want to count overlapping occurrences... maybe this can help

def countOverlapping(string, item):
    count = 0
    for i in range(0,len(string)):
        if item in string[i:len(item)+i]:
            count += 1
    return count

print(countOverlapping("ehehe", "ehe"))

output should be...

How does that work?

as @SomeDude mentioned it uses what he calls a sliding window approach

we take the length of the substring and check if its in that "window" of the string each iteration:

is ehe in [ehe]he? yes, count += 1
is ehe in e[heh]e? no, pass
is ehe in eh[ehe]? yes, count += 1

edited Oct 20 '20 at 14:30

answered Oct 20 '20 at 13:53

Ironkey

2,568
1
8
30

Understood. Thanks Ironkey. – Ralph Yammine Oct 20 '20 at 14:19
No problem, if you liked a particular answer/explanation you can click the green checkmark to accept it for people with this question in the future, thanks for asking! – Ironkey Oct 20 '20 at 14:22

score 0 · Answer 2 · answered Oct 20 '20 at 14:01

You need to go for a sliding window approach to get count of substrings in a string.

example:

string : "ehehehe"

substring : "ehe"

start with first 3 ( because length of substring is 3 ) letters "ehe"- is it the substring we are looking for? - yes.

now leave the first letter "e" and combine letters "he" with the next letter "h" to form "heh" is it the substring we are looking for? - no

now leave the first letter "h" and combine letters "eh" with the next letter "e" to form "ehe" is it the substring we are looking for ? yes

do it till the end of the string and count number of "yes"s

Thanks for the help dude. – Ralph Yammine Oct 20 '20 at 14:20 — Ralph Yammine, Oct 20 '20 at 14:20

How to count number of occurrences of a substring inside a string in Python?

2 Answers2