Updating values in a dictionary

[Thomas]

Greetings

I am having a darn awful time trying to update a matrix:

row = dict([(x,0) for x in range(3)])
matrix = dict([(x,row) for x in range(-3,4,1)])

matrix[2][1] += 1
matrix[-1][2] += 1

"""
Got: a 1 in all col 1 and 2
{-3: {0: 0, 1: 1, 2: 1},
 -2: {0: 0, 1: 1, 2: 1},
 -1: {0: 0, 1: 1, 2: 1},
  0: {0: 0, 1: 1, 2: 1},
  1: {0: 0, 1: 1, 2: 1},
  2: {0: 0, 1: 1, 2: 1},
  3: {0: 0, 1: 1, 2: 1}}
Expected: a 1 in row 2 col 1 and row -1 col 2
{-3: {0: 0, 1: 0, 2: 0},
 -2: {0: 0, 1: 0, 2: 0},
 -1: {0: 0, 1: 0, 2: 1},
  0: {0: 0, 1: 0, 2: 0},
  1: {0: 0, 1: 0, 2: 0},
  2: {0: 0, 1: 1, 2: 0},
  3: {0: 0, 1: 0, 2: 0}}
"""

I must be doing something wrong. Researched and researched. Nothing
clicks.