The following is the recreation of the classic Tetris game with python using pygame, and the following is the game walkthrough.

In the first step, we're just laying the infrastructure of the game; creating an empty window in which the game will be run.

In the second step, we're creating the base grid; using a draw_grid function, we iterate over the x's and y's of the window (columns and rows) and draw our grid where each block is made of a grey square. With the parameters the function takes, the grid dynamically adapts to any changes we make to the window size, number of rows and columns, and the grid size.

In the thrid step, we define each shape to be contained in a 3x3 matrix. For example, a straight shape can be represented as the matrix: [0 1 0 0 1 0 0 1 0] where the 1's are the valid blocks, which can be represented as the list [1, 4, 7]. The same logic follows for the shape's rotation, and for all other shapes. Then we created a Block class, in which the contructor takes the coordinates as parameters, and specifies the shape and the shape variation that we want to pick. The shape function returns the shape from the list of blocks based on the values chosen in the constructor above. Lastly, we created a draw block function that loops in the 3x3 matrix and draws the desired shape on the screen.

In the fourth step we are moving the blocks on the grid. First we are dropping the block from top to bottom, we do that by changing the y coordinates of the block relative to the screen frame rate in the move_block() function. We also set the block to stop moving when it reaches the bottom of the window. Next, we are moving the block to the left or right depending on the user key input. The block stops moving when reaching either edges.

In the fifth step we are creating a board for the game. The board is a list contaning colour values. At first, we initialize it containing all black colours. Then, as an example, when a block reaches the bottom of the screen, we're not going to need it anymore; so we set the block to None, we set its coordinates in the game board to hold the green value, and we draw the game board on the grid as long as the colour is different than black.

In the sixth step we are spawning a new block each time a previous block reaches the bottom of the screen. Each new spawned block shape and position on the screen are randomly picked.

In the seventh step we are rotating the blocks on the key up event. When a player presses the key up, the shape will be changed to the shape that comes right after the current one from the blocks list. The boundaries for the rotation are set as well, as you can't rotate a shape while exceeding the screen boundaries.

In the eightth commit we are testing for block collisions. For that we are creating a collision function that tests if the next step is the bottom edge, left and right edges, or if it's a spot occupied by the game board. We then use that function and replace it in all other functions that needs a collision check.

In the nineth commit we are assigning a random colour to each upcoming block. Also we are setting the game board to preserve the block colour rather than setting it to green.

In the tenth commit we are removing complete lines and diplaying the score on the screen. The find_lines function iterates over the grid and checks if all blocks on that line are part of the game board. If this is true, it means that we hit a full line, and in this case we iterate to replace the current line with the line that's above it; in other words, we remove the current line and push each line above it one block down. We store the removed lines count and use it as the player's score.

In the eleventh and last commit we set the end of the game. The game as we all know, ends when there's no more rooms to spawn new blocks. When that happens we stop the game, freeze the screen and display a game over message. All that happens in the main game loop.

The end :)