after_refactored_find_index_at.py

def find_index(text, pattern):
    """
    Return the starting index of the first occurrence of pattern in text,
    or None if not found.
    """
    
    # if pattern is empty
    if pattern == "":
        return 0
    
    starter = 0 # the starting index of the patterin in the text
    index = 0 # index for text
    subindex = 0 # index for pattern 


    while index <= len(text) - 1:
        
        if text[index] == pattern[subindex]: # char is mathched
            index += 1
            subindex +=1

            if subindex == len(pattern): # check for if we checked all index of patter  
                # starter index of the text where pattern occured 1st time
                return starter  

        else: # mismatch found 
            starter += 1 # shift the starter to next index
            index = starter 
            subindex = 0 # reset the subindex 
        
    return None # pattern not found