Question

allow me to preface this by saying that i am learning python on my own as part of my own curiosity, and i was recommended a free online computer science course that is publicly available, so i apologize if i am using terms incorrectly.

i have seen questions regarding this particular problem on here before – but i have a separate question from them and did not want to hijack those threads. the question:

“a substring is any consecutive sequence of characters inside another string. The same substring may occur several times inside the same string: for example “assesses” has the substring “sses” 2 times, and “trans-Panamanian banana” has the substring “an” 6 times. Write a program that takes two lines of input, we call the first needle and the second haystack. Print the number of times that needle occurs as a substring of haystack.”

my solution (which works) is:

first = str(input())
second = str(input())

count = 0
location = 0
while location < len(second):
   if location == 0:
      location = str.find(second,first,0)
      if location < 0:
         break
      count = count + 1                          
   location = str.find(second,first,location +1)   
   if location < 0:
      break
   count = count + 1
print(count)

if you notice, i have on two separate occasions made the if statement that if location is less than 0, to break. is there some way to make this a ‘global’ condition so i do not have repetitive code? i imagine efficiency becomes paramount with increasing program sophistication so i am trying to develop good practice now.

how would python gurus optimize this code or am i just being too nitpicky?

Answer 1

Check out regular expressions, python’s re module (http://docs.python.org/library/re.html). For example,

import re
first = str(input())
second = str(input())
regex = first[:-1] + '(?=' + first[-1] + ')'
print(len(re.findall(regex, second)))