Create Sequence Diagrams Using seqdiag

Have you ever needed to create sequence diagrams? If you’re like me you constantly have to. Up to now I have always used a manual process using pen/paper or Visio. But I wanted an easier way and found seqdiag.

I installed it in a virtualenv on Ubuntu 14.04.

codeghar@host~$ virtualenv --system-site-packages virt

I used --system-site-packages because seqdiag relies on Python Imaging Library (PIL). Of course, make sure you have python-pil package installed in your OS. I ran into this problem (About the PIL Error — IOError: decoder zip not available) when I didn’t use --system-site-packages. The impression I got was it’s hard to get PIL installed in a virtualenv and easier to just use the system-wide PIL.

codeghar@host~$ source virt/bin/activate

(virt)codeghar@host~$ pip install seqdiag

To create a diagram you need to provide a dialog in a .diag file. You can look at the sample diagrams for more information. The following will create a new file (or overwrite an existing file) called example.png.

(virt)codeghar@host~$ seqdiag -Tpng --no-transparency example.diag

Hat tip to generate uml sequence diagrams with python or perl for bringing seqdiag to my attention.

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