Setting values in matrices - Python

Question

I made i matrix 5x3

field = []
fields = []
    for i in range(0,5):
        for j in range(0,3):
            x = 1
            field.append(x)
    fields.append(field)

When i want to change one field

fields[2][2] = 0

i get this:

fields[0][0] = 1
fields[0][1] = 1
fields[0][2] = **0**
fields[1][0] = 1
fields[1][1] = 1
fields[1][2] = **0**
fields[2][0] = 1
fields[2][1] = 1
fields[2][2] = **0**
fields[3][0] = 1
fields[3][1] = 1
fields[3][2] = **0**
fields[4][0] = 1
fields[4][1] = 1
fields[4][2] = **0**

---

Instead one change i am getting five

Answer 1

Its because you have the reference to the same field across all rows.

You want this:

for i in range(0,5):
    field = []
    for j in range(0,3):
        x = 1
        field.append(x)
    fields.append(field)

field should get reset for every row. That's why you should have it inside the first loop. Now your fields[2][2] = 0 would work.

>>> fields
[[1, 1, 1], [1, 1, 1], [1, 1, 1], [1, 1, 1], [1, 1, 1]]
>>> fields[2][2] = 0
>>> fields
[[1, 1, 1], [1, 1, 1], [1, 1, 0], [1, 1, 1], [1, 1, 1]]