Metadata-Version: 2.1
Name: python-liquid
Version: 0.9.0
Summary: A Python template engine for the Liquid markup language.
Home-page: https://github.com/jg-rp/liquid
License: MIT
Project-URL: API Reference, https://liquid.readthedocs.io/en/latest/api.html
Project-URL: Issue Tracker, https://github.com/jg-rp/liquid/issues
Project-URL: Source Code, https://github.com/jg-rp/liquid
Description: 
        .. _reference documentation: https://shopify.github.io/liquid/
        .. _reference implementation: https://github.com/Shopify/liquid
        .. _dateutil: https://dateutil.readthedocs.io/en/stable/
        .. _asyncpg: https://github.com/MagicStack/asyncpg
        
        
        Python Liquid
        =============
        
        A Python implementation of `Liquid <https://shopify.github.io/liquid/>`_.
        A non evaling templating language suitable for end users.
        
        .. image:: https://img.shields.io/pypi/v/python-liquid.svg
            :target: https://pypi.org/project/python-liquid/
            :alt: Version
        
        .. image:: https://github.com/jg-rp/liquid/actions/workflows/tests.yaml/badge.svg
            :target: https://github.com/jg-rp/liquid/tree/main/tests
            :alt: Tests
        
        .. image:: https://img.shields.io/pypi/l/python-liquid.svg
            :target: https://pypi.org/project/python-liquid/
            :alt: Licence
        
        .. image:: https://img.shields.io/pypi/pyversions/python-liquid.svg
            :target: https://pypi.org/project/python-liquid/
            :alt: Python versions
        
        .. image:: https://img.shields.io/badge/pypy-3.7-blue
            :target: https://pypi.org/project/python-liquid/
            :alt: PyPy versions
        
            
        - `Installing`_
        - `Quick Start`_
        - `API Reference <https://liquid.readthedocs.io/en/latest/api.html>`_
        - `Related Projects`_
        - `Compatibility`_
        - `Benchmark`_
        - `Async Support`_
        - `Custom Filters`_
        - `Custom Tags`_
        - `Custom Loaders`_
        - `Contributing`_
        
        
        Installing
        ----------
        
        Install and update using `pip <https://pip.pypa.io/en/stable/quickstart/>`_:
        
        .. code-block:: text
        
            $ python -m pip install -U python-liquid
        
        
        Quick Start
        -----------
        
        Please see `Shopify's documentation <https://shopify.github.io/liquid/>`_ for template
        syntax and a reference of available tags and filters.
        
        Render a template string by creating a ``Template`` and calling its ``render`` method.
        
        .. code-block:: python
        
            from liquid import Template
        
            template = Template("Hello, {{ you }}!")
            print(template.render(you="World"))  # "Hello, World!"
        
        Keyword arguments passed to ``render`` are added to the `render context`_, and are
        available as variables for templates to use in Liquid expressions.
        
        
        Loading Templates
        *****************
        
        If you want to use the built-in ``include`` or ``render`` tags, you'll need to create an 
        ``Environment``, with a template ``Loader``, then load and render templates from that
        environment.
        
        This example assumes a folder called ``templates`` exists in the current working
        directory, and that the template file ``index.html`` exists within it.
        
        .. code-block:: python
        
            from liquid import Environment
            from liquid import FileSystemLoader
        
            env = Environment(loader=FileSystemLoader("templates/"))
        
            template = env.get_template("index.html")
            print(template.render(some="variable", other="thing"))
        
        You can create templates from strings using an ``Environment`` too. This is often more
        efficient than using ``Template`` directly.
        
        .. code-block:: python
        
            from liquid import Environment
            env = Environment()
        
            template = env.from_string("""
                <html>
                {% for i in (1..3) %}
                  <p>hello {{ some }} {{ i }}</p>
                {% endfor %}
                </html>
            """)
        
            print(template.render(some="thing"))
        
        
        Render Context
        **************
        
        Among other things, a render context includes namespaces for `global` variables passed
        down from the ``Environment`` and `local` variables assigned with the built-in
        ``{% assign %}`` or ``{% capture %}`` tags.
        
        The ``Environment`` constructor accepts ``globals``, a dictionary of variables made
        available to all templates rendered from that environment. 
        
        .. code-block:: python
        
            from liquid import Environment
        
            env = Environment(globals={"site_name": "Google"})
        
            template = env.from_string("""
                <html>
                <h1>{{ site_name }}</h1>
                {% for i in (1..3) %}
                  <p>hello {{ some }} {{ i }}</p>
                {% endfor %}
                </html>
            """)
        
            print(template.render(some="thing"))
        
        As does ``Template``, ``Environment.get_template`` and ``Environment.from_string``,
        where the dictionary of variables is added to the resulting render context each time you
        call ``render``.
        
        .. code-block:: python
        
            from liquid import Environment
        
            env = Environment()
        
            template = env.get_template("index.html", globals={"page": "home"})
            print(template.render(some="thing"))
        
        
        Strictness
        **********
        
        Templates are parsed and rendered in `strict` mode by default. Where syntax and
        render-time type errors raise an exception as soon as possible. You can change the error
        tolerance mode with the ``tolerance`` argument to the ``Environment`` or ``Template``
        constructor.
        
        Available modes are ``Mode.STRICT``, ``Mode.WARN`` and ``Mode.LAX``.
        
        .. code-block:: python
        
            from liquid import Environment, FileSystemLoader, Mode
        
            env = Environment(
                loader=FileSystemLoader("templates/"),
                tolerance=Mode.LAX,
            )
        
        By default, references to undefined variables are silently ignored. In
        `strict variables` mode, any operation on an undefined variable will raise an
        ``UndefinedError``.
        
        .. code-block:: python
        
            from liquid import Environment, StrictUndefined
        
            env = Environment(
                loader=FileSystemLoader("templates/"),
                undefined=StrictUndefined,
            )
        
        HTML Auto Escape
        ****************
        
        As of version 0.7.4, Python Liquid offers HTML auto-escaping. Where context variables
        are automatically escaped on output. Install optional dependencies for auto-escaping
        using the ``autoescape`` extra.
        
        .. code-block:: text
        
            $ python -m pip install -U python-liquid[autoescape]
        
        Auto-escaping is disabled by default. Enable it by setting the ``Environment`` or 
        ``Template`` ``autoescape`` argument to ``True``.
        
        .. code-block:: python
        
            >>> from liquid import Environment
            >>> env = Environment(autoescape=True)
            >>> template = env.from_string("<p>Hello, {{ you }}</p>")
            >>> template.render(you='</p><script>alert("XSS!");</script>')
            '<p>Hello, &lt;/p&gt;&lt;script&gt;alert(&#34;XSS!&#34;);&lt;/script&gt;</p>'
        
        Mark a string as "safe" by making it ``Markup``.
        
        .. code-block:: python
        
            >>> from liquid import Environment, Markup
            >>> env = Environment(autoescape=True)
            >>> template = env.from_string("<p>Hello, {{ you }}</p>")
            >>> template.render(you=Markup("<em>World!</em>"))
            '<p>Hello, <em>World!</em></p>'
        
        Alternatively use the non-standard ``safe`` filter.
        
        .. code-block:: python
        
            >>> from liquid import Environment
            >>> env = Environment(autoescape=True)
            >>> template = env.from_string("<p>Hello, {{ you | safe }}</p>")
            >>> template.render(you="<em>World!</em>")
            '<p>Hello, <em>World!</em></p>'
        
        Async Support
        *************
        
        Python Liquid supports loading and rendering templates asynchronously. When
        ``Template.render_async`` is awaited, ``render`` and ``include`` tags will load
        templates asynchronously.
        
        .. code-block:: python
        
            import asyncio
            from liquid import Environment, FileSystemLoader
        
            env = Environment(loader=FileSystemLoader("templates/"))
        
            async def coro():
                template = await env.get_template_async("index.html")
                return await template.render_async(you="World")
        
            result = asyncio.run(coro())
        
        Custom template loaders should implement ``get_source_async``. For example,
        ``AsyncDatabaseLoader`` will load templates from a PostgreSQL database using `asyncpg`_.
        
        .. code-block:: python
        
          import datetime
          import functools
        
          import asyncpg
        
          from liquid import Environment
          from liquid.exceptions import TemplateNotFound
          from liquid.loaders import BaseLoader
          from liquid.loaders import TemplateSource
        
        
          class AsyncDatabaseLoader(BaseLoader):
              def __init__(self, pool: asyncpg.Pool) -> None:
                  self.pool = pool
        
              def get_source(self, env: Environment, template_name: str) -> TemplateSource:
                  raise NotImplementedError("async only loader")
        
              async def _is_up_to_date(self, name: str, updated: datetime.datetime) -> bool:
                  async with self.pool.acquire() as connection:
                      return updated == await connection.fetchval(
                          "SELECT updated FROM templates WHERE name = $1", name
                      )
        
              async def get_source_async(
                  self, env: Environment, template_name: str
              ) -> TemplateSource:
                  async with self.pool.acquire() as connection:
                      source = await connection.fetchrow(
                          "SELECT source, updated FROM templates WHERE name = $1", template_name
                      )
        
                  if not source:
                      raise TemplateNotFound(template_name)
        
                  return TemplateSource(
                      source=source["source"],
                      filename=template_name,
                      uptodate=functools.partial(
                          self._is_up_to_date, name=template_name, updated=source["updated"]
                      ),
                  )
        
        Custom "drops" can implement ``__getitem_async__``. If an instance of a drop that
        implements ``__getitem_async__`` appears in a ``render_async`` context,
        ``__getitem_async__`` will be awaited instead of calling ``__getitem__``.
        
        Most likely used for lazy loading objects from a database, an async drop would look
        something like this.
        
        .. code-block:: python
        
            class SomeAsyncDrop(abc.Mapping):
                def __init__(self, val):
                    self.key = "foo"
                    self.val = val
        
                def __len__(self):
                    return 1
        
                def __iter__(self):
                    return iter([self.key])
        
                def __getitem__(self, k):
                    # Blocking IO here
                    time.sleep(0.5)
                    # ...
        
                async def __getitem_async__(self, k):
                    # Do async IO here.
                    asyncio.sleep(0.5)
                    # ...
                    
        
        Related Projects
        ----------------
        
        - `django-liquid <https://github.com/jg-rp/django-liquid>`_: A Django template backend
          for Liquid. Render Liquid templates in your Django apps.
        - `Flask-Liquid <https://github.com/jg-rp/Flask-Liquid>`_: A Flask extension for Liquid.
          Render Liquid templates in your Flask applications.
        - `python-liquid-extra <https://github.com/jg-rp/liquid-extra>`_: A growing collection
          of extra tags and filters for Python Liquid. Highlights of which are: 
        
          - an ``if`` tag that supports ``not`` and grouping with parentheses.
          - ``macro`` and ``call`` tags for defining and calling parameterized Liquid snippets.
          - inline ``if``/``else`` expressions. For example ``{{ 'active' if link.active else '' }}``
            or ``{% assign selected = true if product.selected_variant else false %}``.
          - a JSON encoding filter.
        
        Compatibility
        -------------
        
        We strive to be 100% compatible with the `reference implementation`_ of Liquid, written
        in Ruby. That is, given an equivalent render context, a template rendered with Python
        Liquid should produce the same output as when rendered with Ruby Liquid.
        
        Python Liquid faithfully reproduces the following tags.
        
        - assign
        - capture
        - case/when
        - comment
        - cycle
        - decrement
        - echo
        - for/break/continue
        - ifchanged
        - if/elsif/else
        - include
        - increment
        - liquid
        - raw
        - render
        - tablerow
        - unless
        
        Known Issues
        ************
        
        `Please help by raising an issue if you notice an incompatibility.`
        
        - Error handling. Python Liquid might not handle syntax or type errors in the same
          way as the reference implementation. We might fail earlier or later, and will 
          almost certainly produce a different error message.
          
        - The built-in ``date`` filter uses `dateutil`_ for parsing strings to ``datetime``\s,
          and ``strftime`` for formatting. There are likely to be some inconsistencies between
          this and the reference implementation's equivalent parsing and formatting of dates and
          times.
        
        Benchmark
        ---------
        
        You can run the benchmark using ``make benchmark`` (or ``python -O performance.py`` if
        you don't have ``make``) from the root of the source tree. On my ropey desktop computer
        with a Ryzen 5 1500X, we get the following results.
        
        .. code-block:: text
        
            Best of 5 rounds with 100 iterations per round and 60 ops per iteration (6000 ops per round).
            
            lex template (not expressions): 1.3s (4727.35 ops/s, 78.79 i/s)
                             lex and parse: 6.4s (942.15 ops/s, 15.70 i/s)
                                    render: 1.7s (3443.62 ops/s, 57.39 i/s)
                     lex, parse and render: 8.2s (733.30 ops/s, 12.22 i/s)
        
        And PyPy3.7 gives us a decent increase in performance.
        
        .. code-block:: text
        
            Best of 5 rounds with 100 iterations per round and 60 ops per iteration (6000 ops per round).
        
            lex template (not expressions): 0.58s (10421.14 ops/s, 173.69 i/s)
                             lex and parse: 2.9s (2036.33 ops/s, 33.94 i/s)
                                    render: 1.1s (5644.80 ops/s, 94.08 i/s)
                     lex, parse and render: 4.2s (1439.43 ops/s, 23.99 i/s)
        
        
        On the same machine, running ``rake benchmark:run`` from the root of the reference
        implementation source tree gives us these results.
        
        .. code-block:: text
        
            /usr/bin/ruby ./performance/benchmark.rb lax
        
            Running benchmark for 10 seconds (with 5 seconds warmup).
        
            Warming up --------------------------------------
                         parse:     3.000  i/100ms
                        render:     8.000  i/100ms
                parse & render:     2.000  i/100ms
            Calculating -------------------------------------
                         parse:     39.072  (± 0.0%) i/s -    393.000  in  10.058789s
                        render:     86.995  (± 1.1%) i/s -    872.000  in  10.024951s
                parse & render:     26.139  (± 0.0%) i/s -    262.000  in  10.023365s
        
        I've tried to match the benchmark workload to that of the reference implementation, so
        that we might compare results directly. The workload is meant to be representative of
        Shopify's use case, although I wouldn't be surprised if their usage has changed subtly
        since the benchmark fixture was designed.
        
        Custom Filters
        --------------
        
        Add a custom template filter to an ``Environment`` by calling its ``add_filter`` method.
        A filter can be any callable that accepts at least one argument (the result of the left 
        hand side of a filtered expression), and returns a string or object with a ``__str__``
        method.
        
        Here's a simple example of adding ``str.endswith`` as a filter function.
        
        .. code-block:: python
        
          from liquid import Environment, FileSystemLoader
        
          env = Environment(loader=FileSystemLoader("templates/"))
          env.add_filter("endswith", str.endswith)
        
        And use it like this.
        
        .. code-block:: text
        
            {% assign foo = "foobar" | endswith: "bar" %}
            {% if foo %}
                <!-- do something -->
            {% endif %}
        
        
        Decorate filter functions with ``with_context`` or ``with_environment`` to have the 
        active context or environment passed as a keyword arguments.
        
        .. code-block:: python
        
          from liquid.filter import with_context
          from liquid.filter import string_filter
        
          @string_filter
          @with_context
          def link_to_tag(label, tag, *, context):
              handle = context.resolve("handle", default="")
              return (
                  f'<a title="Show tag {tag}" href="/collections/{handle}/{tag}">{label}</a>'
              )
        
        And register it wherever you create your environment.
        
        .. code-block:: python
        
          from liquid import Environment, FileSystemLoader
          from myfilters import link_to_tag
        
          env = Environment(loader=FileSystemLoader("templates/"))
          env.add_filter("link_to_tag", link_to_tag)
        
        In a template, you could then use the ``link_to_tag`` filter like this.
        
        .. code-block::
        
            {% if tags %}
                <dl class="navbar">
                <dt>Tags</dt>
                    {% for tag in collection.tags %}
                    <dd>{{ tag | link_to_tag: tag }}</dd>
                    {% endfor %}
                </dl>
            {% endif %}
        
        All built-in filters are implemented in this way, so have a look in
        ``liquid/builtin/filters/`` for many more examples.
        
        Note that old style, class-based filters are depreciated and will be removed in Liquid
        0.9. You can still implement custom filters as callable classes, but Liquid will not
        include any abstract base classes for filters or legacy filter "helpers".
        
        
        Custom Tags
        -----------
        
        Register a new tag with an ``Environment`` by calling its ``add_tag`` method. All tags
        must  inherit from ``liquid.tag.Tag`` and implement its ``parse`` method.
        
        ``parse`` takes a single argument of type ``TokenStream`` that wraps an iterator of
        ``Token``\s, and returns an ``ast.Node`` instance. More often than not, a new subclass
        of ``ast.node`` will accompany each ``Tag``. These ``Node``\s make up the parse tree,
        and are responsible for writing rendered text to the output stream via the required
        ``render_to_output`` method.
        
        Here's the implementation of ``UnlessTag``, which parses a boolean expression and a
        block of statements before returning a ``UnlessNode``.
        
        .. code-block:: python
        
            class UnlessTag(Tag):
        
                name = TAG_UNLESS
                end = TAG_ENDUNLESS
        
                def parse(self, stream: TokenStream) -> Node:
                    parser = get_parser(self.env)
        
                    expect(stream, TOKEN_TAG, value=TAG_UNLESS)
                    tok = stream.current
                    stream.next_token()
        
                    expect(stream, TOKEN_EXPRESSION)
                    expr_iter = tokenize_boolean_expression(stream.current.value)
                    expr = parse_boolean_expression(TokenStream(expr_iter))
        
                    stream.next_token()
                    consequence = parser.parse_block(stream, ENDUNLESSBLOCK)
        
                    expect(stream, TOKEN_TAG, value=TAG_ENDUNLESS)
        
                    return UnlessNode(
                        tok=tok,
                        condition=expr,
                        consequence=consequence
                    )
        
        Things worthy of note: 
        
        - Block tags (those that have a start and end tag with any number of statements in
          between) are expected to leave the stream with their closing tag as the current token.
        
        - The template lexer does not attempt to tokenize tag expressions. It is up to the
          ``Tag`` to tokenize and parse its expression, if any, possibly using or extending a
          built-in expression lexer found in ``liquid.lex``.
        
        - The ``expect`` and ``expect_peek`` helper functions inspect tokens from the stream and
          raise an appropriate exception should a token's type or value not meet a tag's
          expectations.
        
        - You can find parsers for common expression types in ``liquid.parse``, all of which
          return a ``liquid.expression.Expression``. ``Expression``\s have an
          ``evaluate(context)`` method for use from ``ast.Node.render_to_output``.
        
        
        All built-in tags are implemented in this way, so have a look in
        ``liquid/builtin/tags/`` for examples. 
        
        Custom Loaders
        --------------
        
        Write a custom loader class by inheriting from ``liquid.loaders.BaseLoader`` and
        implementing its ``get_source`` method. Here we implement ``DictLoader``, a loader that
        uses a dictionary of strings instead of the file system for loading templates.
        
        .. code-block:: python
        
            from liquid.loaders import BaseLoader
            from liquid.loaders import TemplateSource
            from liquid.exceptions import TemplateNotFound
        
            class DictLoader(BaseLoader):
                def __init__(self, templates: Mapping[str, str]):
                    self.templates = templates
        
                def get_source(self, _: Env, template_name: str) -> TemplateSource:
                    try:
                        source = self.templates[template_name]
                    except KeyError as err:
                        raise TemplateNotFound(template_name) from err
        
                    return TemplateSource(source, template_name, None)
        
        ``TemplateSource`` is a named tuple containing the template source as a string, its name
        and an optional ``uptodate`` callable. If ``uptodate`` is not ``None`` it should be a
        callable that returns ``False`` if the template needs to be loaded again, or ``True``
        otherwise.
        
        You could then use ``DictLoader`` like this.
        
        .. code-block:: Python
        
            from liquid import Environment
            from liquid.loaders import DictLoader
        
            snippets = {
                "greeting": "Hello {{ user.name }}",
                "row": """
                    <div class="row"'
                      <div class="col">
                        {{ row_content }}
                      </div>
                    </div>
                    """,
            }
        
            env = Environment(loader=DictLoader(snippets))
            
            template = env.from_string("""
                <html>
                  {% include 'greeting' %}
                  {% for i in (1..3) %}
                    {% include 'row' with i as row_content %}
                  {% endfor %}
                </html>
            """)
        
            print(template.render(user={"name": "Brian"}))
        
        Contributing
        ------------
        
        .. _Pylance: https://marketplace.visualstudio.com/items?itemName=ms-python.vscode-pylance
        .. _Pyright: https://github.com/microsoft/pyright
        
        - Install development dependencies with `Pipenv <https://github.com/pypa/pipenv>`_
        
        - Python Liquid fully embraces type hints and static type checking. I like to use the
          `Pylance`_ extension for Visual Studio Code, which includes `Pyright`_ for static type
          checking.
        
        - Format code using `black <https://github.com/psf/black>`_.
        
        - Write tests using ``unittest.TestCase``.
        
        - Run tests with ``make test`` or ``python -m unittest``.
        
        - Check test coverage with ``make coverage`` and open ``htmlcov/index.html`` in your
          browser.
        
        - Check your changes have not adversely affected performance with ``make benchmark``.
        
Platform: UNKNOWN
Classifier: Development Status :: 4 - Beta
Classifier: Intended Audience :: Developers
Classifier: License :: OSI Approved :: MIT License
Classifier: Programming Language :: Python :: 3
Classifier: Programming Language :: Python :: 3.7
Classifier: Programming Language :: Python :: 3.8
Classifier: Programming Language :: Python :: 3.9
Classifier: Programming Language :: Python :: 3.10
Classifier: Programming Language :: Python :: Implementation :: CPython
Classifier: Programming Language :: Python :: Implementation :: PyPy
Requires-Python: >=3.7
Description-Content-Type: text/x-rst
Provides-Extra: autoescape
