Question

I can’t quite figure out what’s going on with string templates:

t = Template('cannot teach an ${dog.old} ${tricks.new}. ${why} is this ${not} working')
print t.safe_substitute({'dog.old': 'old dog', 'tricks.new': 'new tricks', 'why': 'OH WHY', 'not': '@#%@#% NOT'})

This prints:

cannot teach an ${dog.old} ${tricks.new}. OH WHY is this @#%@#% NOT working

I thought that the braces handled arbitrary strings. What characters are allowed in braces and is there any way I can subclass Template to do what I want?

Answer 1

From the documentation…

$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.

The period is a non-identifier character, and braces are simply used to separate the identifier from adjacent non-identifier text.