Legacy preprocessors

Sites can define custom preprocessors to do pretty much anything at build time and run time. Custom preprocessors can leverage all of the builtin preprocessor controls, such as the grow preprocess command, the --preprocess flag, and options like name, autorun, and tags.

Specify and use your custom preprocessor in podspec.yaml:

# podspec.yaml

  - ext.hello.HelloPreprocessor

- kind: hello
  person: Zoey

Define the preprocessor in the /ext/ folder. Grow preprocessors should subclass grow.Preprocessor and use ProtoRPC Messages to define their configuration.

# /ext/hello.py

import grow
from protorpc import messages

class HelloPreprocessor(grow.Preprocessor):
    """Says hello to a person."""

    KIND = 'hello'

    class Config(messages.Message):
        person = messages.StringField(1)

    def run(self, build=True):
        print 'Hello, {}!'.format(self.config.person)

Lastly, in the same /ext folder, create an empty file called __init__.py to let Grow know that this is a module.

Now, you can use the preprocessor.

$ grow preprocess
Hello, Zoey!