unsure of how 2-d lists work in python

Question

Need to make a 6x8 matrix. In this matrix, need to assign values to various cells within the matrix and then simulate a heating/cooling system. Before I get there though, I need to make sure this is right. Is this how you make rows and columns? Does it matter that it does not display this way when printed? Like I said I need to assign values to each of theses cells, does it matter that some already have a value by the way I made the lists? Is there a way to make the list without any initial values?

matrix = [] # Create an empty list
numberOfRows = 6
numberOfColumns = 8
for row in range(0, numberOfRows):
    matrix.append([]) # Add an empty new row
    for column in range(0, numberOfColumns):
        matrix[row].append(column)

print(matrix) 



[[0, 1, 2, 3, 4, 5, 6, 7], [0, 1, 2, 3, 4, 5, 6, 7], [0, 1, 2, 3, 4, 5, 6, 7], [0, 1, 2, 3, 4, 5, 6, 7], [0, 1, 2, 3, 4, 5, 6, 7], [0, 1, 2, 3, 4, 5, 6, 7]]

Answer 1

Yes, it is a good method. However, it is much easier and more pythonic to use list comprehension : matrix = [list(range(numberOfColumns)) for _ in range(numberOfRows)]

And yes, you can make a list with no value : [] or list()

And even a 2-dimensional list : [[]]

However, it has no use.

Answer 2

You can use this way to make 2D arrays, but a few comments:

• You may consider initializing the elements to 0 (or -1) by changing the last line to matrix[row].append(0) . This is mostly a design choice. For example, if, in your program, later on you do not change the values at every position, then you will be left with old values from the initialization.
• You can re-write range(0, numberOfRows) to range(numberOfRows) ; it starts from 0 by default.
• List comprehension, as Labo has already mentioned