jinja2-embedded 0.1.4
Jinja2 template loader for embedded Python runtimes
Requires Python: >=3.10
Keywords: bundler, embedded, executable, jinja2, pyoxidizer, python

jinja2-embedded
===============

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Template loader for embedded python runtimes, e.g., `PyOxidizer <https://github.com/indygreg/PyOxidizer>`_ or `PyInstaller <https://github.com/pyinstaller/pyinstaller>`_.

The main problem with the current `PackageLoader <https://jinja.palletsprojects.com/en/3.0.x/api/#jinja2.PackageLoader>`_ is that it can only load templates from packages which are installed and materialized as directories.
However, when using a bundler from above, the resources, i.e., templates, are embedded into the executable.
Thus, the :code:`PackageLoader` will throw the following exception: :code:`The package was not installed in a way that PackageLoader understands`.

The :code:`EmbeddedPackageLoader` from this package fixes this problem and required minimal changes.
Under the hood, we utilize the :code:`Loader` and :code:`ResourceReader` implementation of the package provided through `importlib <https://docs.python.org/3/library/importlib.html>`_.
Thereby, the :code:`EmbeddedPackageLoader` will work when the package is normally installed as directory and in an embedded environment.

How to use
^^^^^^^^^^

Two changes are necessary.
First, change :code:`PackageLoader` to :code:`EmbeddedPackageLoader`:

.. code::

    from jinja2 import Environment, PackageLoader
    from jinja2_embedded import EmbeddedPackageLoader

    # before
    env = Environment(
        loader=PackageLoader('my_package', 'templates'),
        autoescape=True,
        ...
    )

    # after
    env = Environment(
        loader=EmbeddedPackageLoader('my_package.templates'),
        autoescape=True, # default False, but FastAPI uses True as default
        extensions=[],
    )

    # with FastAPI
    from fastapi.templating import Jinja2Templates
    templates = Jinja2Templates(env=env)

Second, declare the `templates` directory as a module by adding a :code:`__init__.py` file:

.. code::

    my_package
    ├── __init__.py
    ├── main.py
    └── templates
        ├── __init__.py # required
        ├── bar
        │   ├── __init__.py # not required
        │   └── test.html.jinja2
        ├── foo
        │   └── test.html
        └── test.html


The subdirectories inside the `templates` directory can be declared as modules (here :code:`my_package.templates.bar`), but this is not required.
The :code:`EmbeddedPackageLoader` works with either or mixed configuration.

How it works
^^^^^^^^^^^^

The :code:`EmbeddedPackageLoader` will first try to locate the template with the :code:`ResourceReader` from :code:`my_package.templates`.
From our example above, the :code:`ResourceReader` is able to see:

.. code::

    >>> from importlib.util import find_spec
    >>> package = 'my_package.templates'
    >>> loader = find_spec(package).loader
    >>> resource_reader = loader.get_resource_reader(package)
    >>> contents = resource_reader.contents()
    >>> print(list(contents))
    ['foo/test.html', 'test.html']


So we can use the provided :code:`resource_reader` to read either of those files:

.. code::

    >>> with resource_reader.open_resource('foo/test.html') as file:
    ...    content = file.read()
    >>> print(content.decode('utf-8'))
    FOO

Since, :code:`bar` is declared as module (directory contains a :code:`__init__.py` file), we need to use the :code:`ResourceReader` of the respective module:

.. code::

    >>> resource_reader = loader.get_resource_reader('my_package.templates.bar')
    >>> contents = resource_reader.contents()
    >>> print(list(contents))
    ['test.html.jinja2']

The :code:`EmbeddedPackageLoader` will first try to find the resource in the :code:`ResourceReader` of the main package and then fallback to the :code:`ResourceReader` of the submodule (if it is declared as such).

Development
^^^^^^^^^^^

Install `rye <https://github.com/astral-sh/rye>`_, then run :code:`rye sync`. This creates a `venv <https://docs.python.org/3/library/venv.html>`_ with all necessary dependencies.
Run :code:`pytest` to run all tests.

To run the tests in a embedded Python version created with `PyOxidizer <https://github.com/indygreg/PyOxidizer>`_, run :code:`pyoxidizer run` in the root directory.
After the executable has been build, the tests will run automatically.

This repository used `ruff <https://github.com/astral-sh/ruff>`_ to enforce style standards. The formatting is automatically done for you via `pre-commit <https://pre-commit.com/>`_.
Install pre-commit with :code:`pre-commit install`.