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Graphviz with Django and Creole

This page describes just another creole macro which renders graphviz instructions from a creole page into an image.

The macro is included by the instruction.

digraph G {Hello->World}

As with mathplot there are optional parameters.

  • title that defines the title and alt attributes of the <img> tag
  • show_source is False by default. If True the content of the graph source is displayed

Here is the simple test example.

G Hello Hello World World Hello->World

Rendering a dot macro is a two tier process.

  1. When the creole markup language is translated the macro gives the HTML code of an <img> tag and the graph source is stored temporarily into the database. The key to that database is the src attribute of the <img> tag.
  2. When rendering the image the graph source is taken from the database and stored temporarily into a file, rendered to a png image file. Both temporary files are removed after the procedure returned the image to the server.
G cluster0 User cluster1 Django cluster2 Database a Browser request page b HTML with IMG tag a->b c Browser request image d Render image c->d e Browser display all b->c g Graph definition source b->g d->e f Creole markup source f->b g->d

The Creole Macro

The graph source is taken from the macro's body and stored with a unique key into the database.

[Error: Wrong macro arguments: "py" for macro 'code' (maybe wrong macro tag syntax?)]

The Graphviz View

The vie translates the graphviz source into a png image and returns the image as a HttpResponse object. As the the translation is accomplished by a system call to the dot routine, the files have to be stored temporarily. That process require 3 external prerequisites.

  1. The installation of graphviz
  2. The command to launch the dot routine settings.GRAPHVIZ_DOT_CMD. (On a linux platform you can use the "whereis dot" command to locate it.)
  3. A temporary directory should exist somewhere settings.GRAPHVIZ_TMP_DIR. Write permissions have to be granted to the server.

For convenience i stored the latter two parameters in my setting.

[Error: Wrong macro arguments: "py" for macro 'code' (maybe wrong macro tag syntax?)]

And this is the view code.

[Error: Wrong macro arguments: "py" for macro 'code' (maybe wrong macro tag syntax?)]

Tags: Software


(c) Mato Nagel, Weißwasser 2004-2020, Disclaimer