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

if __name__ == "__main__":
    print get_indices("abcabcabc", "bc"), "sb", [1,4,7]
    print get_indices("bbbbbbb", "bb"), "sb", [0,1,2,3,4,5]
    print get_indices("bbbbbbb", "aa"), "sb", []
    print get_indices("abc", "abcde"), "sb", []
    print get_indices("", ""), "sb", [0]
    print get_indices("abcabcabc", "ab"), "sb", [0,3,6]