Can I create 2d or 3d matrices just by declaring it's elements one by 1 in loop like a[i][j] by looping I and j? (In python)

Answer 1

I think so. What’s the context?

In Python I think when you create a list, it starts as an empty list. So you would be appending, not assigning, in the loop:

a = []
i = 0
while i < 10:
a.append([])
j = 0
while j < 5:
a[i].append(input())
j += 1
i += 1

Answer 2

I would recommend nested loops. First for first dimension, second - for second and so on.