Joe Lanman

I ran into an issue today while trying to implement image uploads. It’s a very basic implementation: taking files from a POST request, copying them to a local folder, and then making thumbnails of them.

I started with the file upload tutorial in the web.py cookbook.

The problem I was getting was that the Python Image library (PIL) was failing to make the thumbnails, with the error ‘image file is truncated’.

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After looking at Web.py’s own templating system, and considering Cheetah, I’ve ended up going with Mako for now. So far I’ve found it very straightforward, with some powerful-looking features to expand into in the future.

One of the great features is template inheritance – but I hit an issue recently with passing a variable from a child template to a parent. It’s not immediately obvious how to do this, but I found the answer on the Mako Google Groups archive (link here):

Child:

<%inherit file="meta.html"/>

<%def name="vars()">

	<% return (meta.id,) %>

</%def>

Parent:

<% (id,) = self.vars() %>

On a side note, I found out today that two of the Python libraries I’m using, Mako and SQLAlchemy, were coded by the same guy – Michael Bayer. Clever chap – not only are the libraries pretty impressive, but they are both well documented and he regularly contributes to the mailing lists for both projects. And he doesn’t even have a big internet head like some developers – though I tracked his blog down here:

http://techspot.zzzeek.org/

Should that be ‘a’ or ‘an’ SQLAlchemy object?

My current CMS project is based on creating templates in the back-end, and then using these to produce ‘inherited’ objects with the same attributes.

I quickly found that it’s surprisingly tricky to grab a template object using SQLAlchemy, and copy it into a similar, but separate, entity. Using the Python ‘copy’ function confuses SQLAlchemy – when you try to save it, it thinks it is merely a representation of the original (template) object.

Here’s how I create separate ‘clones’ from my template objects, defining a function on the object itself:

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The Python language has useful string methods to search for prefixes and suffixes:

my_string.startswith('pre')

The same thing can be achieved in Javascript using the rather powerful search and replace methods.

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