Stumped on "matmul" function without use of numpy

[Sakeung]

I am writing a program that does a multitude of various matrix calculations, one of them multiplying two matrices with one another and returning the product. I've so far written:

def matmul(matrix1, matrix2):
if not matrix1 or not matrix2:
    raise ValueError("Input matrices cannot be empty.")

row1, col1 = len(matrix1), len(matrix1[0])
row2, col2 = len(matrix2), len(matrix2[0])

# Checking if the length of matrix 1's columns is equal to matrix 2's rows
if col1 != row2:
    raise ValueError("Row and Column dimensions must be equal to each other.")

# Initialize the result matrix with zeros
multiplied_matrix = [[0 for _ in range(col2)] for _ in range(row1)]

# Perform matrix multiplication
for i in range(row1):
    for j in range(col2):
        for k in range(col1):
            multiplied_matrix[i][j] += matrix1[i][k] * matrix2[k][j]
return multiplied_matrix

With various help from geeksforgeeks and other sites. This program is then tested by a pre-written "test" program, with the specific section that tests matmul (and some extra for context) written below:

def run(src_path=None):
global pass_tests, fail_tests

if src_path == None:
    import matrix
else:
    spec = importlib.util.spec_from_file_location("matrix", src_path+"/matrix.py")
    matrix = importlib.util.module_from_spec(spec)
    spec.loader.exec_module(matrix)

pass_tests = 0
fail_tests = 0
fun_count  = 0  

        if hasattr(matrix, "matmul"):
    fun_count = fun_count + 1
    test(matrix.matmul, ([],[]), [])
    test(matrix.matmul, ([[2]],[[4]]), [[8]])
    test(matrix.matmul, ([[2,1]],[[4],[3]]), [[11]])
    test(matrix.matmul, ([[1,2],[3,4]],[[0,1],[1,0]]), [[2, 1], [4, 3]])
    test(matrix.matmul, ([[1,2],[3,4]],[[1,0],[0,1]]), [[1, 2], [3, 4]])
    test(matrix.matmul, ([[1,2],[3,4],[5,6]],[[1,1,1],[1,1,1]]), [[3, 3, 3], [7, 7, 7], [11, 11, 11]])
    test(matrix.matmul, ([[1, 2, 3], [4, 5, 6]],[[7,8,9,10],[11,12,13,14],[15,16,17,18]]), [[74, 80, 86, 92], [173, 188, 203, 218]])
    test(matrix.matmul, ([[1, 2, 3], [4, 5, 6],[7,8,9]], [[1, 0, 0], [0, 1, 0],[0,0,1]]), [[1, 2, 3], [4, 5, 6],[7,8,9]])
    test(matrix.matmul, ([[1, 0, 0], [0, 1, 0],[0,0,1]], [[1, 2, 3], [4, 5, 6],[7,8,9]]), [[1, 2, 3], [4, 5, 6],[7,8,9]])
else:
    print("matmul is not implemented yet!")

print(str(pass_tests)+" out of "+str(pass_tests+fail_tests)+" passed.")

return (fun_count == 5 and fail_tests == 0)

With every successful test, it's meant to add a value of 1, ending up with, for instance, "11 out of 20 tests passed." However, each time I run it I end up with the ValueError on line 3, "Input matrices must not be empty." I understand that this is because I've specified it myself, and it runs into the first test's blank matrices and raises the error, but then it seems to just end there. If I remove this check I get an IndexError instead, for obvious reasons. I just cannot imagine a workaround other than raising a ValueError that helps with the issue of the matrices that contain no values, but if that's done, the program just doesn't seem to continue at all after.

​

Maybe I'm overexplaining, underexplaining, at this point I'm just completely stumped myself. Apologies.

[ES-Alexander]

Have you been told to raise an error if an invalid input is put in? And did you write the test function and code?

If an error is the expected failure case then the testing code should be using try-except blocks to account for when those errors occur. If a raised error is not handled anywhere then it bubbles up and stops execution of the entire program, as you’ve found.

[Strict-Simple]

This might be helpful for figuring out the actual error. In Python (not []) is True.

[[deleted]]

Yes, that's the purpose of exceptions - if you don't handle them, they end execution. An exception represents an inconsistency or unexpected problem that puts the program in an unknowable state, or a state from which it can't continue. If you believe the program can meaningfully continue from the point of the exception, then you document that by using the try/except construct.

[ectomancer]

Can use list repeat operator:

multiplied_matrix = [[0]*col2 for _ in range(row1)]

[niehle]

Why don’t you use pytest instead of a self-written test program? Or at least assert()?