linear_backward.py

def linear_backward(dZ, cache):
    
    A_prev, W, b = cache
    m = A_prev.shape[1]

    dW = (1 / m) * np.dot(dZ, cache[0].T)  
    db = (1/m) * np.sum(dZ, axis=1, keepdims=True)
    dA_prev = np.dot(cache[1].T, dZ)
    
    assert (dA_prev.shape == A_prev.shape)
    assert (dW.shape == W.shape)
    assert (db.shape == b.shape)
    
    return dA_prev, dW, db