Looking for a pattern in a list

Question

I've created this function that looks for sequences in a list. If [1,2,3] exists, it will print True. I've tested the code and it works fine.

def looking_patt(pattern,cursor,found):
 big_s = []
 for i in range(1,101):
 if i % 10 == 0:
 big_s.extend([1,2,3])
 else:
 big_s.append(i)
 # check control
 print(big_s)
 for i in big_s:
 if i == pattern[cursor]:
 cursor += 1
 if cursor == len(pattern):
 found.append(pattern)
 print(found)
 cursor = 0
 else:
 cursor = 0 
 print(len(found) > 0) 

Part of the script (the for i in big_s:) has been taken from an answer in this SO question.

How can it be improved?

Answer 1

I guess that the first part of your code is just to initialize the sample data.

Then here are a few things:

• Separate initialization and main loop. I know this is just an exercise, but always doing it will help you keep the mindset.
• If you only need to count something, just count it. Don't keep track of everything.
• If you only need to check the existence of something, use a boolean value and return as soon as you've found it. Adding elements to a list so that at the end you can count them and return a boolean based on the count is definitely not an efficient way to do it.
• What you call cursor is actually an integer, not an object, so the name index may be more appropriate
• If you want to give the chance to start searching from a specific index, you may also want to have a default value for that parameter (0 looks like a good choice)
• You don't need the third parameter, that's what you are going to return

This is my attempt at it:

big_s = []
def init_big_s():
 for i in range(1,101):
 if i % 10 == 0:
 big_s.extend([1,2,3])
 else:
 big_s.append(i)
def looking_patt(pattern, index=0):
 for i in big_s:
 if i == pattern[index]:
 index += 1
 if index == len(pattern):
 return True
 else:
 index = 0 
 return False
init_big_s()
print looking_patt([1, 2, 3])

• Andy K: Hi @chatterone, thanks for your feedback. ok for separating the functionS, this is what I did initially but I said to myself Hey why not put everything into one umbrella? Can you explain a bit more If you only need to check the existence of something, use a boolean value and return as soon as you've found it. Adding elements to a list so that at the end you can count them and return a boolean based on the count is definitely not an efficient way to do it. this part?
• ChatterOne: @AndyK if you don't need to compute something, just don't do it :-) If the purpose of the function was to return the patterns that you found, you may have had a point. But if all you need is a check that the pattern exists, just return True as soon as the first pattern is found, no need to save the elements.