ExtensionLoaderMixin

Complexity

Total Complexity

6

Size/Duplication

Total Lines	44
Duplicated Lines	0 %

Importance

Changes

0

2 Methods

Rating	Name	Duplication	Size	Complexity
A	_read_extensions()	0	12	4
B	__init__()	0	24	2

# -*- coding: utf-8 -*-

"""Jinja2 environment and extensions loading."""

from jinja2 import Environment, StrictUndefined

from .exceptions import UnknownExtension


class ExtensionLoaderMixin(object):
    """Mixin providing sane loading of extensions specified in a given context.

    The context is being extracted from the keyword arguments before calling
    the next parent class in line of the child.
    """

    def __init__(self, **kwargs):
        """Initialize the Jinja2 Environment object while loading extensions.

        Does the following:

        1. Establishes default_extensions (currently just a Time feature)
        2. Reads extensions set in the cookiecutter.json _extensions key.
        3. Attempts to load the extensions. Provides useful error if fails.
        """
        context = kwargs.pop('context', {})

        default_extensions = [
            'cookiecutter.extensions.JsonifyExtension',
            'jinja2_time.TimeExtension',
        ]
        extensions = default_extensions + self._read_extensions(context)

        try:
            super(ExtensionLoaderMixin, self).__init__(
                extensions=extensions,
                **kwargs
            )
        except ImportError as err:
            raise UnknownExtension('Unable to load extension: {}'.format(err))

    def _read_extensions(self, context):
        """Return list of extensions as str to be passed on to the Jinja2 env.

        If context does not contain the relevant info, return an empty
        list instead.
        """
        try:
            extensions = context['cookiecutter']['_extensions']
        except KeyError:
            return []
        else:
            return [str(ext) for ext in extensions]


class StrictEnvironment(ExtensionLoaderMixin, Environment):
    """Create strict Jinja2 environment.

    Jinja2 environment will raise error on undefined variable in template-
    rendering context.
    """

    def __init__(self, **kwargs):
        """Set the standard Cookiecutter StrictEnvironment.

        Also loading extensions defined in cookiecutter.json's _extensions key.
        """
        super(StrictEnvironment, self).__init__(
            undefined=StrictUndefined,
            **kwargs
        )