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])