GRAPH THEORY and longest path calculation with python

I have a list of nodes and values between nodes; Values can be positive and negative. There will be 100 Nodes with many DIRECTIONAL connections (Node A ---> Node B doesn't mean Node B ---> Node A). Here is an example: Node A ---> Node B (value 4) Node A ---> Node C (value 12) Node B ---> Node P (value -5) Node F ---> Node C (value 1) ... I want a python program to 'accurately guess' the most valuable path between two selected nodes Example: Input: Entry node: A Exit node: U Output: Max value: 324 Solution: Node A ---> Node B ---> Node Z ---> Node G ---> Node U Please write GRAPHTHEORY in your quote so that I understand that you read the project. Otherwise your bid will be ignored. The money is released after delivering a code for the problem stated above. I will test with some random nodes and values (Python or Perl preferred)