Polish

segments.py

 #!/usr/bin/env python3
 
-# segmentation
-#   OUTPUT: a graph-tool "gt" file (change name as needed)
+"""Collapses the input graph into a new graph: the graph of
+segments. An edge of the graph is a segment. The new graph is output
+in the binary format of graph-tool.
+
+"""
 
 import graph_tool
 import time