Expanding templates

PEP 292 defines a simplified string template, where substitution variables are identified by a leading $-sign. The substitution dictionary names the keys and values that should be interpolated into the template:

>>> key_1 = 'key_1'
>>> key_2 = 'key_2'

>>> from flufl.i18n import expand
>>> # This may fail for Python < 2.6.5
>>> print(expand(
...     '$key_2 is different than $key_1', {
...         key_1: 'the first key',
...         key_2: 'the second key',
...         }))
the second key is different than the first key

See issue 4978 for Python 2.6.x compatibility.