# (Uses str.find.)
def get_indices(text, substr):
    '''Return a list containing the indices where str substr appears in str
    text.  Overlapping instances of substr should be counted.  For example,
    get_indices("abcabcabc", "bc") --> [1, 4, 7]
    get_indices("bbbbbbb", "bb") --> [0, 1, 2, 3, 4, 5]'''

    # Accumulate the indices of occurrences here.
    indices = []
    # The position of the next occurrence of substr within text.
    index = text.find(substr, 0)
    
    # Keep looking until there are no more occurrences.
    while index != -1:
        # Record this occurrence.
        indices.append(index)
        # Advance past this occurrence and look for the next one.
        index = text.find(substr, index + 1)
        
    return indices

# (Does not use str.find.)
def basic_stringmatch(text, pattern):
    '''Find all instances of the string pattern in the string 
    text.  Return a list containing the starting indices of all
    matches.  
    
    This version iterates through text one character at a time, 
    checking if the pattern matches starting at that character.
    It checks the entire pattern at each character.'''
    
    matches = []
    pattern_length = len(pattern)
    
    # Iterate through text
    for index in range(len(text) - pattern_length + 1):
        
        # Check if the pattern matches starting at this character
        match = True
        for match_index in range(pattern_length):
            if text[index + match_index] != pattern[match_index]:
                match = False            
        if match:
            matches.append(index)

    return matches


def early_exit_stringmatch(text, pattern):
    '''Find all instances of the string pattern in the string 
    text.  Return a list containing the starting indices of all
    matches.  
    
    This version iterates through text one character at a time, 
    checking if the pattern matches starting at that character.
    It stops checking the pattern when a mismatch is detected.'''
    
    matches = []
    pattern_length = len(pattern)
    
    # Iterate through text
    for index in range(len(text) - pattern_length + 1):
        
        # Check if the pattern matches starting at this character
        match_index = 0
        while match_index < pattern_length and \
              text[index + match_index] == pattern[match_index]:
            match_index = match_index + 1
            
        # The pattern matches if the previous loop iterated through
        # the entire pattern.
        if match_index == pattern_length:
            matches.append(index)

    return matches

if __name__ == '__main__':

    funs = (get_indices,basic_stringmatch,early_exit_stringmatch)
    for f in funs:
        print f,f("abcabcabc", "bc"), "sb", [1,4,7]
        print f,f("bbbbbbb", "bb"), "sb", [0,1,2,3,4,5]
        print f,f("bbbbbbb", "aa"), "sb", []
        print f,f("abc", "abcde"), "sb", []
        print f,f("", ""), "sb", [0]
        print f,f("abcabcabc", "ab"), "sb", [0,3,6]    
        print f,f("CTACAATATATCGTATCATATCC","ATATC"), "sb",[7,17]
        print f,f("ATATAT","AT"), "sb", [0,2,4]