Kruskal's Algorithm in Python

Question

I have learnt about graph theory lately and i m trying to implement Kruskal's algorithm to find the min. spanning tree in a graph using a weight matrix.I got a correct output for a matrix and an out of bound error for another! It gave me an error for:

[[1000,16,12,21,1000,1000,1000],[16,1000,1000,17,20,1000,1000],[12,1000,1000,28,1000,31,1000],[21,17,28,1000,18,19,23],[1000,20,1000,18,1000,1000,11],[1000,1000,31,19,1000,1000,27],[1000,1000,1000,23,11,27,1000]]

Matrix for which i got a correct answer is the one below: (NOTE:1000 is used to denote a weight of infinity

vertices=5
spset=[True]*5
wt=[[1000,1,3,4,1000],[1,1000,5,1000,7],[3,5,1000,6,8],[4,1000,6,1000,2],[1000,7,8,2,1000]]


row=[0]

for i in xrange(vertices-1):
  row_num,col_num,min_no=-1,-1,1000
  for i in row:
    temp=min(wt[row[i]])
    if(min_no>temp):
      min_no=temp
      row_num=i
      col_num=wt[i].index(temp)
  print str(min_no)+"("+str(row_num)+","+str(col_num)+")"
  spset[col_num]=False
  wt[col_num][row_num]=1000
  for i in xrange(vertices):
    wt[i][col_num]=1000
  row.append(col_num)

d=raw_input()

Answer 1

In the following code block,

for i in row:
    temp=min(wt[row[i]])

i is being iterated over elements of row. If row has two elements [0,2], then when i becomes 2, row[i] will give an IndexError: list index out of range.

If you want to iterate over elements of row, use for i in range(len(row)) instead.