### Introduction ###
This is a simple example to illustrate the use of python-graph. This should give you a feel about how the API is.
For the proper API documention, check this [link](http://dl.dropboxusercontent.com/u/1823095/python-graph/docs/index.html).
### Code ###
```
#!/usr/bin/env python
# Copyright (c) 2007-2008 Pedro Matiello
# License: MIT (see COPYING file)
# Import graphviz
import sys
sys.path.append('..')
sys.path.append('/usr/lib/graphviz/python/')
sys.path.append('/usr/lib64/graphviz/python/')
import gv
# Import pygraph
from pygraph.classes.graph import graph
from pygraph.classes.digraph import digraph
from pygraph.algorithms.searching import breadth_first_search
from pygraph.readwrite.dot import write
# Graph creation
gr = graph()
# Add nodes and edges
gr.add_nodes(["Portugal","Spain","France","Germany","Belgium","Netherlands","Italy"])
gr.add_nodes(["Switzerland","Austria","Denmark","Poland","Czech Republic","Slovakia","Hungary"])
gr.add_nodes(["England","Ireland","Scotland","Wales"])
gr.add_edge(("Portugal", "Spain"))
gr.add_edge(("Spain","France"))
gr.add_edge(("France","Belgium"))
gr.add_edge(("France","Germany"))
gr.add_edge(("France","Italy"))
gr.add_edge(("Belgium","Netherlands"))
gr.add_edge(("Germany","Belgium"))
gr.add_edge(("Germany","Netherlands"))
gr.add_edge(("England","Wales"))
gr.add_edge(("England","Scotland"))
gr.add_edge(("Scotland","Wales"))
gr.add_edge(("Switzerland","Austria"))
gr.add_edge(("Switzerland","Germany"))
gr.add_edge(("Switzerland","France"))
gr.add_edge(("Switzerland","Italy"))
gr.add_edge(("Austria","Germany"))
gr.add_edge(("Austria","Italy"))
gr.add_edge(("Austria","Czech Republic"))
gr.add_edge(("Austria","Slovakia"))
gr.add_edge(("Austria","Hungary"))
gr.add_edge(("Denmark","Germany"))
gr.add_edge(("Poland","Czech Republic"))
gr.add_edge(("Poland","Slovakia"))
gr.add_edge(("Poland","Germany"))
gr.add_edge(("Czech Republic","Slovakia"))
gr.add_edge(("Czech Republic","Germany"))
gr.add_edge(("Slovakia","Hungary"))
# Draw as PNG
dot = write(gr)
gvv = gv.readstring(dot)
gv.layout(gvv,'dot')
gv.render(gvv,'png','europe.png')
```
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```
# Then, draw the breadth first search spanning tree rooted in Switzerland
st, order = breadth_first_search(gr, root="Switzerland")
gst = digraph()
gst.add_spanning_tree(st)
dot = write(gst)
gvv = gv.readstring(dot)
gv.layout(gvv,'dot')
gv.render(gvv,'png','europe-st.png')
```
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