如何用Python中的边缘格计数特定单词的出现

Question

I have written the code to count the occurrence of a certain word cat in it, the code is passing only some of my test cases, it is not passing all the test, especially the edge cases. Please note am not allowed to use inbuilt functions like count() and a whole host of others. Here is my code:

mystery_string = "my cat your cat"
splitword = mystery_string.split()
sum = 0
for string in splitword:
    if string == "cat":
        sum += 1
print (sum)

when i change the variable mystery_string to mystery_string = "catcatcatcatcat!!". or mystery_string = "cacacat cacacat" or this one mystery_string = "ucatX" or even this mystery_string = ".$cacacatcatcat". the code just breaks. i have researched stackoverflow for similar problem but no solution.

Answer 1

Use the count method of strings.

>>> "catcatcatcatcat!!".count("cat")
5

Or, using regular expressions :

>>> import re
>>> len(re.findall("cat", "catcatcatcatcat!!"))
5

Answer 2

Actually there is the ".count(str)" function Ex:

catcatcat!ccat".count("cat")

Outputs 4 But if you don't want to use it you can do the following

def count(mainstr, substr):
 thecount = 0
 for i in range(len(mainstr)):
  if i <= len(mainstr) - len(substr):
   if mainstr[i:i+len(substr)] == substr:
    thecount+=1
 return thecount

Your code counts the occurrence of a word in a text but not the occurrence of a word in a string...