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A package for finding the best path through a network graph

Project description


Fastpath is a fast and lightweight tool for finding the shortest path in a weighted graph. As input it only needs the starting node, the ending node, and the weights of each node to node edge. For versatility it uses the Bellman-Ford algorithm, which allows for negative weights. Future version will incorporate the Dijkstra algorithm to speed up runtimes on graphs that do not contain negative edges. To install fastpath,

git clone
cd fastpath; make

The only library dependency for fastpath is uthash (which is included). The fastpathz has the extra dependency of mini-gmp (which is included).

There are two flavors of fastpath. The first is the default fastpath, which will work for 99% of needed cases. It's limitation is that it uses the C-type long double for edge weights, which can cause rounding errors if you have extremely large/small numbers for edge weights (ie -1E50 or 1E50). This is because during the path relaxation step of the Bellmanford code, C cannot distinguish a difference between 1E50 and 1E50 + 1 If your numbers are extremely large/small, then you can use the fastpathz version, which uses infinite-precision integers as edge weights. The downside of using fastpathz is that decimal places get dropped, so the C code does not distinguish between 1 and 1.1. This limitation can partially be overcome by just multiplying all your weights by an arbitrary number.

Fastpath Example

Run either flavor on the included sample data:

fastpath --source A --target Z < edges.txt 
fastpathz --source A --target Z < edges.txt 

The output of either command is the path of nodes, and should look like


The structure of the graph looks like:

A -----> B -----> C <----- F
         |        |
         |        |
         v        v
         D -----> E -----> Z
  • Strings can be used for the nodes, and the weights can be positive or negative long double numbers. The weights can even be in the form of scientific shorthand (1.6E+9).

Python Example

FastPath is now also available as a PIP package available at

It is installable by simply using pip

pip install fastpath 

To use in your python code, first import the module, write edges to the graph, and then provide a beginning node (source) and an end node (target)

import fastpath as fp

f = open("edges.txt", "r")
for line in f:
        ret = fp.add_edge(line)

for edge in fp.get_path(source="A", target="Z"):

Output is the path of nodes, and should look like

$ python 

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