def get_column(puzzle: str, col_num: int) -> str:
    """Return column col_num of puzzle.

    Precondition: 0 <= col_num < number of columns in puzzle

    >>> get_column('abcd\nefgh\nijkl\n', 1)
    'bfj'
    """

    puzzle_list = puzzle.strip().split('\n')
    column = ''
    for row in puzzle_list:
        column += row[col_num]

    return column