def previous_unwrittable_on_row(view, coords):
    """Return position of the previous (in row) letter that is unwrittable"""
    x, y = coords
    minx = -1
    for offset in range(x - 1, minx, -1):
        letter = view[offset, y]
        if letter not in REWRITABLE_LETTERS:
            return offset
    return None
Return position of the previous (in row) letter that is unwrittable