Using special chars in Python string Templates

Posted on Wed 05 June 2013 in Python

PEP-292 introduced a nice Python templating feature.
Templates placehoder names are subject to some restrictions,Documentation says:

$identifier names a substitution placeholder matching a mapping key of "identifier".
By default, "identifier" must spell a Python identifier.
The first non-identifier character after the $ character terminates this placeholder specification.

This means that \${placeholder} names must spell the Python identifier syntax: dots (.), hyphen (-) or other special chars are not allowed.
The default regex that must match the placeolder is:

r'[\_a-z][\_a-z0-9]\*'

You can simply extend this regex overwriting the idpattern property in Template class.

Here a quick example:

>>> from string import Template
>>> class MyTemplate(Template):
...     idpattern = r'[a-z][\.\-_a-z0-9]*'
... 
>>> MyTemplate("a=${ciccio_pippo-b}").substitute({'ciccio_pippo-b': "pasticcio"})
'a=pasticcio'
>>>