Follow PEP 8 - Code lay-out - Imports

Overlap/edgelist_to_Graphviz.py

 #!/usr/bin/env python3
 
 import csv
-import pygraphviz as pgv
 import sys
 
+import pygraphviz as pgv
+
 if len(sys.argv) != 3:
     sys.exit("Required arguments: input-edgelist output-Graphviz")