Now our program has the ability to play any sound. But we don't just need to play a single sound. We need to play a pattern. Let's define a method called play_pattern, which reads our internal data structure and plays files accordingly (see code 3.06.py):

import time
    def play_pattern(self):
        self.now_playing = True
        while self.now_playing:
            play_list = self.get_is_button_clicked_list()
            num_columns = len(play_list[0])
            for column_index in range(num_columns):
                column_to_play = self.get_column_from_matrix(
                      play_list, column_index)
                for i, item in enumerate(column_to_play):
                    if item:
                        sound_filename = self.get_drum_file_path(i)
                        self.play_sound(sound_filename)
                time.sleep(self.time_to_play_each_column())
                if not self.now_playing: break
            if not self.loop: break 
        self.now_playing = False

We also add an associated method that returns the i^th column from a matrix:

def get_column_from_matrix(self, matrix, i):
  return [row[i] for row in matrix]

The description of the preceding code is as follows:

• We create a class attribute called self.keep_playing to decide whether the pattern is to be played just once or continuously in a loop.

• We create another class attribute called self.now_playing to track whether a beat is currently playing. This will help us to make some decisions on how to handle a sudden close of program or change of pattern by the user.

• We then fetch the two-dimensional Boolean list from our data structure and scan each column of the list to look for True values. We get the column data from the matrix by defining a separate method called get_column_from_matrix(self, matrix, i).

• For every column, if a True value is encountered, we fetch the corresponding drum file path and call the self.play_sound() method to play the file.

• The code sleeps for a fixed duration of time before reading the second column. This sleep duration defines the tempo of the drum beat. If the code does not sleep for some time between each column, all the patterns would play almost immediately and would not even sound like a rhythm. We need to import the time module to use the time.sleep() method.

• The amount of time the code sleeps between scanning each column is decided by another method called self.time_to_play_each_column(), which we define next.