def size_of_ins(statement):
    """Returns the size (in words) of the instruction."""
    # Note: the LC-3 is word-addressable, not byte-addressable, so a two-byte
    # instruction has a size of 1, not 2.
    # There is a variant called the LC-3b which is byte-addressable.
    if statement.statement_type == 'INSTRUCTION':
        # All LC-3 instructions are 2 bytes (size of 1).
        return 1
    elif statement.statement_type == 'DIRECTIVE':
        if statement.directive_type == 'FILL':
            return 1
        elif statement.directive_type == 'BLKW':
            return statement.size
        elif statement.directive_type == 'STRINGZ':
            byte_count = len(statement.value) + 1
            word_count = int(byte_count / 2)
            return word_count
    return None