Font size for edge label

edit

This one took me some time. It can be achieved by opening YOUR_SAGE_DIR/local/lib/python2.6/site-packages/sage/graphs/graph_plot.py and changing the line

self._plot_components['edge_labels'].append(text(str(edges_to_draw[(a,b)][0][0]),[(self._pos[a][0]+self._pos[b][0])/2., (self._pos[a][1]+self._pos[b][1])/2.]))

to

self._plot_components['edge_labels'].append(text(str(edges_to_draw[(a,b)][0][0]),[(self._pos[a][0]+self._pos[b][0])/2., (self._pos[a][1]+self._pos[b][1])/2.],fontsize=20))

There is no need to compile anything, just save the file and then run sage.

Remark: in the mentioned file there are 5 lines starting with

self._plot_components['edge_labels'].append(text...

so to be on the safe side you can change all of them (adding fontsize=20 as a last parameter to the text function). I suspect they handle different situations (directed/undirected graphs, etc.). You can put DEFAULT_FONTSIZE = 20 at the beginning of the file and then add fontsize=DEFAULT_FONTSIZE to the text functions - this will allow you to change the size easily later.