How do I use inheritance in Cheetah templates?

Question

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?

Answer 1

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.