How do I use inheritance in Cheetah templates?

For Cheetah3, there is a very rough documentation of the inheritance feature: http://cheetahtemplate.org/users_guide/inheritanceEtc.html#extends

But I don't get how to make it actually work.

Let's assume I have two template files:

A.tmpl

#def message
Hello Cheetah
#end def
This is an example: $message

B.tmpl

#extends A
#def message
Hello Cheetah with Inheritance
#end def

and a simple driver program such as:

from Cheetah.Template import Template

t = Template(file='B.tmpl')
print t

Obviously, that doesn't work, because there is no class A when executing this code.

But how does it go? Or is inheritance only possible with precompiled Cheetah templates?

There are two ways to import one template from the other.

1. Compile all templates to *.py files using cheetah compile command line program. Then import works at the Python level.

To semi-automatically compile all templates after you edit them I recommend the following Makefile (GNU flavour):

.SUFFIXES: # Clear the suffix list
.SUFFIXES: .py .tmpl

%.py: %.tmpl
        cheetah compile --nobackup $<
        python -m compile $@

templates = $(shell echo *.tmpl)
modules = $(patsubst %.tmpl,%.py,$(templates))

.PHONY: all
all: $(modules)

(Don't forget — makefiles require indent with tabs, not spaces.)

2. Subvert Python import to make Cheetah import directly from *.tmpl files.

Code:

from Cheetah import ImportHooks
ImportHooks.install()

import sys
sys.path.insert(0, 'path/to/template_dir')  # or sys.path.append

PS. ImportHooks automatically try to import from *.pyc, *.py and *.tmpl — whatever is found first. A few days ago I extended ImportHooks to automatically compile *.tmpl to *.py and *.pyc. I'm going to write more docs and push in a few days. Expect the final release Cheetah 3.2 in a few months.