jinjanator-plugins

jinjanator-plugins: API package for jinjanator plugins

jinjanator can be extended through the use of plugins; these are Python packages installed into the same environment as the tool itself, which use special markers to 'hook' into various features. There is a minimal example in the plugin_example directory which demonstrates three of the four possible hooks.

For a more complete example, intended for publication, check out the jinjanator-plugin-ansible repository.

Plugins can provide:

• formats: data parsers used to extract data from input files.

• filters: functions used in Jinja2 templates to transform data.

• tests: functions used in Jinja2 templates to make decisions in conditional logic.

• globals: functions used in Jinja2 templates to obtain data from external sources.

• extensions: Jinja2 extensions that can add extra filters, tests, globals or even extend the parser.

For more details on the functionality and requirements for 'filters', 'tests', 'globals', and 'extensions', refer to the Jinja2 documentation.

Installation

Normally there is no need to install this package; instead it should be listed as one of the dependencies for the plugin package itself.

Note: It is strongly recommended to pin the dependency for this package to a specific version, or if not, a "year.release" version range (like "23.2.*"). Failure to pin to a very narrow range of versions may result in breakage of a plugin when the API is changed in a non-backward-compatible fashion.

This is somewhat similar to semantic versioning, except not that :)

Basic structure

A minimal plugin consists of two files:

• pyproject.toml: provides package and project information, and build instructions

• Python source: provides functions to implement the desired features, and hook markers to plug them into jinjanator

pyproject.toml

[build-system]
build-backend = "setuptools.build_meta"
requires = [
  "setuptools>=61",
]

[project]
name = "jinjanator-plugin-example"
version = "0.0.0"
dependencies = [
  "jinjanator-plugins==23.3.0",
]

[tool.setuptools]
py-modules = ["jinjanator_plugin_example"]

[project.entry-points.jinjanator]
example = "jinjanator_plugin_example"

build-system

Any PEP517-compatible build system can be used, for this simple example setuptools is being used.

project

The name and version are required to build a package containing the plugin. Note the specific version dependency on the jinjanator-plugins package.

tool.setuptools

This section tells setuptools to include a single source file (not a package directory) into the distribution. Note that this is a module name, not a file name, so there is no .py extension.

project.entry-points.jinjanator

This is the first part of the 'magic' mechanism which allows jinjanator to find the plugin. The entry here (which can use any name, but should be related to the project name in order to avoid conflicts) creates an 'entry point' which jinjanator can use to find the plugin; the value is the name of the module which jinjanator should import to find the plugin's hooks (and must match the name specified in the tool.setuptools section).

jinjanator_plugin_example.py

import codecs

from jinjanator_plugins import (
    FormatOptionUnknownError,
    FormatOptionUnsupportedError,
    FormatOptionValueError,
    plugin_filters_hook,
    plugin_formats_hook,
    plugin_identity_hook,
    plugin_tests_hook,
    plugin_extensions_hook,
)


def rot13_filter(value):
    return codecs.encode(value, "rot13")


def is_len12_test(value):
    return len(value) == 12


class SpamFormat:
    name = "spam"
    suffixes = (".spam",)
    option_names = ("ham",)

    def __init__(self, options):
        self.ham = False

        if options:
            for option in options:
                if option == "ham":
                    self.ham = True

    def parse(self, data_string):
        if self.ham:
            return {
                "ham": "ham",
                "cheese": "ham and cheese",
                "potatoes": "ham and potatoes",
            }

        return {
            "spam": "spam",
            "cheese": "spam and cheese",
            "potatoes": "spam and potatoes",
        }


@plugin_identity_hook
def plugin_identities():
    return "example"


@plugin_filters_hook
def plugin_filters():
    return {"rot13": rot13_filter}


@plugin_tests_hook
def plugin_tests():
    return {"len12": is_len12_test}


@plugin_formats_hook
def plugin_formats():
    return {SpamFormat.name: SpamFormat}


@plugin_extensions_hook
def plugin_extensions():
    return ['jinja2.ext.debug']

Note that the real example makes use of type annotations, but they have been removed here for simplicity.

Imports

The imports from jinjanator_plugins are necessary for the plugin to:

• Mark the hooks it wishes to use to provide additional features.
• Construct one (or more) Format objects to describe the formats it supports, if any.
• Raise option-related exceptions from its format function, if any.

rot13_filter

A simple filter function which applies the rot13 transformation to the string value it receives.

is_len12_test

A simple test function which returns True if the value it receives has length 12.

SpamFormat

A class providing a simple format function which ignores the content provided (which jinjanator would have read from a data file), and instead returns one of two canned responses based on whether the ham option has been provided by the user.

The parse method is the function which does the work; the __init__ method handles options provided by the user; the class attributes provide details of the format.

plugin_identities

The hook function which will be called by jinjanator to allow this plugin to identify itself; the @plugin_identities_hook decorator marks the function so that it will be found.

The function must return a string, which can contain any information needed to identify the plugin. This should include the plugin's name and version, and can include versions of any packages on which it depends.

This string will be included in the output generated by jinjanate --version, so it should not include any newlines or other formatting characters.

Note that the function must be named plugin_identities; it is the second part of the 'magic' mechanism mentioned above.

plugin_filters

The hook function which will be called by jinjanator to allow this plugin to register any filter functions it provides; the @plugin_filters_hook decorator marks the function so that it will be found.

The function must return a dictionary, with each key being a filter function name (the name which will be used in the Jinja2 template to invoke the function) and the corresponding value being a reference to the function itself.

Note that the function must be named plugin_filters; it is the second part of the 'magic' mechanism mentioned above.

plugin_tests

The hook function which will be called by jinjanator to allow this plugin to register any test functions it provides; the @plugin_tests_hook decorator marks the function so that it will be found.

The function must return a dictionary, with each key being a test function name (the name which will be used in the Jinja2 template to invoke the function) and the corresponding value being a reference to the function itself.

Note that the function must be named plugin_tests; it is the second part of the 'magic' mechanism mentioned above.

plugin_formats

The hook function which will be called by jinjanator to allow this plugin to register any format functions it provides; the @plugin_formats_hook decorator marks the function so that it will be found.

The function must return a dictionary, with each key being a format function name (the name which will be used in the --format argument to jinjanator, if needed) and the corresponding value being a class which implements the requirements of the Format protocol (defined in init.py).

In particular these requirements include:

• a class attribute called name which contains the name of the format (for use in error messages)

• a class attribute called 'suffixes' which contains a (possibly empty) list of file suffixes which can be matched to this format during format auto-detection

• a class attribute called 'option_names' which contains a (possibly empty) list of options which the user can provide to modify the parser's behavior

• a constructor method (__init__) which accepts a (possibly empty) list of options provided by the user, and performs any validation needed on them, storing the results in the self object

• a parse method which accepts a (possibly empty) string containing the input data, and parses it according to the format's needs, using any previously-validated options stored in the self object

Note that the hook function must be named plugin_formats; it is the second part of the 'magic' mechanism mentioned above.

Format classes can accept 'options' to modify their behavior, and should raise the exceptions listed below, when needed, to inform the user if one of the provided options does not meet the format's requirements.

• FormatOptionUnknownError will be raised automatically by the jinjanator CLI based on the content of the option_names attribute of the format class.

• FormatOptionUnsupportedError should be raised when a provided option is not supported in combination with the other provided options or with the parsed data.

• FormatOptionValueError should be raised when a provided option has a value that is not valid.

plugin_extensions

The hook function which will be called by jinjanator to allow this plugin to register any additional Jinja2 extensions; the @plugin_extensions_hook decorator marks the function so that it will be found.

The function must return a list, with each entry being a string (the name of a Jinja2 extension that should be added to the Jinja2 Environment).

Those strings should correspond to extensions that themselves are available in your python installation and available for Jinja2 to locate.

Some examples:

• Jinja2 own debug extension: jinja2.ext.debug
• Jinja-Markdown: jinja_markdown.MarkdownExtension
• jinja-markdown2: jinja2_markdown.MarkdownExtension
• https://github.com/topics/jinja2-extension etc...

Note that the function must be named plugin_extensions; it is the second part of the 'magic' mechanism mentioned above.

Release Information

Backwards-incompatible Changes

• Added support for Python 3.13, and removed support for Python 3.8.

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