Odtnhj

I'm stuck with pset6 similarities more. When I want to insert the tuples into my matrix, I keep getting the message 'NoneType' object does not support item assignment. If I change none to 0 or to (None, None), I get the same message : int/tuple object does not support item assignment. What am I overlooking?

def distances(a, b):
"""Calculate edit distance from a to b"""

# create matrix of dimensions len(a) + 1 and len(b) + 1 and fill with zeros
matrix = [[None for i in range(len(b) + 1)] for j in range(len(a) + 1)]

matrix[0][0] = (0, None)

for x in range (1, len(a) + 1):
 matrix[x][0] = (x, Operation.INSERTED)

for y in range (1, len(b) + 1):
 matrix[0][y] = (y, Operation.DELETED)

for x in range(1, len(a) + 1):
 for y in range(1, len(b) + 1):
 if a[x - 1] == b[y - 1]:
 matrix[x][y] = (min(matrix[x - 1][y - 1][0], matrix[x][y - 1][0], matrix[x - 1][y][0]), None)
 else:
 matrix[x][y][0] = min(matrix[x - 1][y - 1][0] + 1, matrix[x][y - 1][0] + 1, matrix[x - 1][y][0] + 1)

 if matrix[x][y][0] == matrix[x - 1][y - 1][0] + 1:
 matrix[x][y][1] = Operation.SUBSTITUTED
 if matrix[x][y][0] == matrix[x][y - 1][0] + 1:
 matrix[x][y][1] = Operation.INSERTED
 else:
 matrix[x][y][1] = Operation.DELETED

return matrix

The tuple object does not support item assignment error message means Python tuples can't be changed in-place, but they can be overlaid by new tuples. Try creating a new tuple and assigning it to matrix[x][y], rather than assigning the tuple elements themselves.