--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/docs/tutorial/mypandocfilters/graphviz-file.py	Mon Jan 08 11:46:53 2018 +0100
@@ -0,0 +1,37 @@
+#!/usr/bin/env python
+
+"""
+Pandoc filter to process code blocks with class "graphviz" into
+graphviz-generated images.
+
+Needs pygraphviz
+"""
+
+import os
+import sys
+
+import pygraphviz
+
+from pandocfilters import toJSONFilter, Para, Image, get_filename4code, get_caption, get_extension, get_value
+
+def graphviz(key, value, format, _):
+    if key == 'CodeBlock':
+        [[ident, classes, keyvals], file] = value
+        if "graphviz-file" in classes:
+            caption, typef, keyvals = get_caption(keyvals)
+            prog, keyvals = get_value(keyvals, u"prog", u"dot")
+            filetype = get_extension(format, "svg", html="svg", latex="pdf")
+            with open(file) as f:
+                code = f.read()
+            dest = get_filename4code("graphviz", code, filetype)
+
+            if not os.path.isfile(dest):
+                g = pygraphviz.AGraph(string=code)
+                g.layout()
+                g.draw(dest, prog=prog)
+                sys.stderr.write('Created image ' + dest + '\n')
+
+            return Para([Image([ident, ['graphviz'], keyvals], caption, [dest, typef])])
+
+if __name__ == "__main__":
+    toJSONFilter(graphviz)