Accessing nodes of networkx graph in python

Question

I want to access and store nodes of networkx graph and then do further processing on it. I have following code:

for node in vis:    
    for a,b in G[node]:
        print a,b

This code gives following Error : Traceback (most recent call last):[1]

  File "C:\Users\Mrinal\workspace\algo_asgn1\prims.py", line 29, in <module>
    for a,b in G[node]:
TypeError: 'int' object is not iterable

whereas when i write:

for node in vis:
        print G[node]

I get following output which I suppose is a dictionary with key as destination node and weight of the connection as value.

{2: {'weight': 5}, 3: {'weight': 2}, 4: {'weight': 2}}
{2: {'weight': 5}, 3: {'weight': 2}, 4: {'weight': 2}}
{2: {'weight': 5}, 3: {'weight': 2}, 4: {'weight': 2}}
{2: {'weight': 5}, 3: {'weight': 2}, 4: {'weight': 2}}
{2: {'weight': 5}, 3: {'weight': 2}, 4: {'weight': 2}}

My graph has following data:

1 2 5
1 3 2
2 3 4
2 4 6
1 4 2

What mistake am I doing over here? Can someone please suggest me changes. Thanks

Answer 1

G[node] is a dictionary. Iterating over a dictionary gives you the keys of that dictionary , which in this case are the integers 2,3,4 . Thus, if you run this snippet you get the following output:

>>> for a in {2: {'weight': 5}, 3: {'weight': 2}, 4: {'weight': 2}}:
...     print a
... 
2
3
4

The problem you're having stems from the fact that you are trying to iterate over two variables -- for a, b in x -- where x is an integer and thus can't split into two separate variables. Instead, just use a single variable to get the node, eg

>>> node = {2: {'weight': 5}, 3: {'weight': 2}, 4: {'weight': 2}}
>>> for a in node:
...     print a, node[a]
... 
2 {'weight': 5}
3 {'weight': 2}
4 {'weight': 2}

Answer 2

I figured out what I was doing wrong here that i did not use .iteritems()

for node in vis:    
    for a,b in G[node].iteritems():
        print a,b