Python 3: finding a set of letters in a string using loops

Question

i'm using python 3 and i would like to know how to count the amount of times a set of 3 letters comes up in a sentence:

con = ""
count = 0
for i in mystery_string:
    if i == "c":
        con = "c" 
    if i == "a" and con == "c":
        con = "ca"   
    if i == "t" and con == "ca":
        con = "cat"
    if con == "cat":
        count +=1
        con = ""
print (count)

this is the code i have so far, however it doesn't seem to work for every case can someone help me

the thing i also need to explain is that i cannot use the builtin function count()

Possible duplicate of [Count the number occurrences of a character in a string](https://stackoverflow.com/questions/1155617/count-the-number-occurrences-of-a-character-in-a-string) — Muzol, Nov 24 '18 at 18:13

score 2 · Answer 1 · answered Nov 24 '18 at 18:10

2

just do the following

mystery_string.count('cat')

answered Nov 24 '18 at 18:10

Biswadip Mandal

534
1
4
15

1

It is a good solution for this specific word, however the count() method does not support overlapping – prophet-five Nov 24 '18 at 18:38
1

you mean examples like if I am counting 'aba' in 'gtfababacd' ? – Biswadip Mandal Nov 24 '18 at 18:41
sure, np, I recently encountered this problem myself :) – prophet-five Nov 24 '18 at 18:47

score 1 · Accepted Answer · answered Nov 24 '18 at 18:14

1

you can use slicing:

word='cat'
count = 0
for i in range(len(mystery_string)-len(word)+1):
    if mystery_string[i:i+len(word)]==word:
        count +=1
print (count)

answered Nov 24 '18 at 18:14

prophet-five

509
3
14

this solution supports overlapping, contrary to count() function, for example the word 'pop' will be counted once in the string 'popop' if you use the count function – prophet-five Nov 24 '18 at 18:17

score 0 · Answer 3 · answered May 17 '20 at 12:46

mystery_string = "my cat your cat"

count = 0

current_search_letter = "c"


    if letter == "c":
        current_search_letter = "a"


    elif letter == "a" and current_search_letter == "a":
        current_search_letter = "t"


    elif letter == "t" and current_search_letter == "t":
        count += 1
        current_search_letter = "c"
    else:
        current_search_letter = "c"
print(count)

Python 3: finding a set of letters in a string using loops

3 Answers3