Pycon 2014 Thumbtack solution ("dense" version)

tetris_dense.py

import sys, re #thumbtack pycon tetris challenge. "dense" solution by @mattboehm
def shift_down(col):#shift piece down 1 space
    loc = "".join(col[::-1])
    space = loc.find("#") - 1 
    return col if loc == -2 else list(loc[:space] + loc[space+1:] + ".")[::-1]
def top_row_blank(board):#check if the top row has only .
    return all(tile == "." for tile in board[0])
def find_piece(board):#Replace the X's for the piece with #
    board, marked_board = board[:], []
    while top_row_blank(board):#skip top blank rows
        marked_board.append(board.pop(0))
    while not top_row_blank(board):#for each row with a piece, replace X's
        marked_board.append(board.pop(0).replace("X", "#"))
    return marked_board + board #board is >=1 blank row followed by ground
if __name__ == '__main__':
    board = [list(row) for row in find_piece([line.rstrip("\n") for line in sys.stdin.readlines()])]
    while not any(col[-1]=="#" or "#X" in "".join(col) for col in zip(*board)):
        board = zip(*(shift_down(col) for col in zip(*board)))
    print len([row for row in board if "." not in row])