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Pystache

Pystache is a Python implementation of Mustache. Mustache is a framework-agnostic, logic-free templating system inspired by ctemplate and et. Like ctemplate, Mustache "emphasizes separating logic from presentation: it is impossible to embed application logic in this template language."

The mustache(5) man page provides a good introduction to Mustache's syntax. For a more complete (and more current) description of Mustache's behavior, see the official Mustache spec.

Pystache is semantically versioned and can be found on PyPI. This version of Pystache passes all tests in version 1.1.2 of the spec.

Requirements

Pystache is tested with--

  • Python 2.4 (requires simplejson version 2.0.9 or earlier)
  • Python 2.5 (requires simplejson)
  • Python 2.6
  • Python 2.7
  • Python 3.1
  • Python 3.2
  • Python 3.3
  • PyPy

Distribute (the setuptools fork) is recommended over setuptools, and is required in some cases (e.g. for Python 3 support). If you use pip, you probably already satisfy this requirement.

JSON support is needed only for the command-line interface and to run the spec tests. We require simplejson for earlier versions of Python since Python's json module was added in Python 2.6.

For Python 2.4 we require an earlier version of simplejson since simplejson stopped officially supporting Python 2.4 in simplejson version 2.1.0. Earlier versions of simplejson can be installed manually, as follows:

pip install 'simplejson<2.1.0'

Official support for Python 2.4 will end with Pystache version 0.6.0.

Install It

pip install pystache

And test it--

pystache-test

To install and test from source (e.g. from GitHub), see the Develop section.

Use It

>>> import pystache
>>> print pystache.render('Hi {{person}}!', {'person': 'Mom'})
Hi Mom!

You can also create dedicated view classes to hold your view logic.

Here's your view class (in .../examples/readme.py):

class SayHello(object):
    def to(self):
        return "Pizza"

Instantiating like so:

>>> from pystache.tests.examples.readme import SayHello
>>> hello = SayHello()

Then your template, say_hello.mustache (by default in the same directory as your class definition):

Hello, {{to}}!

Pull it together:

>>> renderer = pystache.Renderer()
>>> print renderer.render(hello)
Hello, Pizza!

For greater control over rendering (e.g. to specify a custom template directory), use the Renderer class like above. One can pass attributes to the Renderer class constructor or set them on a Renderer instance. To customize template loading on a per-view basis, subclass TemplateSpec. See the docstrings of the Renderer class and TemplateSpec class for more information.

You can also pre-parse a template:

>>> parsed = pystache.parse(u"Hey {{#who}}{{.}}!{{/who}}")
>>> print parsed
[u'Hey ', _SectionNode(key=u'who', index_begin=12, index_end=18, parsed=[_EscapeNode(key=u'.'), u'!'])]

And then:

>>> print renderer.render(parsed, {'who': 'Pops'})
Hey Pops!
>>> print renderer.render(parsed, {'who': 'you'})
Hey you!

Python 3

Pystache has supported Python 3 since version 0.5.1. Pystache behaves slightly differently between Python 2 and 3, as follows:

  • In Python 2, the default html-escape function cgi.escape() does not escape single quotes. In Python 3, the default escape function html.escape() does escape single quotes.
  • In both Python 2 and 3, the string and file encodings default to sys.getdefaultencoding(). However, this function can return different values under Python 2 and 3, even when run from the same system. Check your own system for the behavior on your system, or do not rely on the defaults by passing in the encodings explicitly (e.g. to the Renderer class).

Unicode

This section describes how Pystache handles unicode, strings, and encodings.

Internally, Pystache uses only unicode strings (str in Python 3 and unicode in Python 2). For input, Pystache accepts both unicode strings and byte strings (bytes in Python 3 and str in Python 2). For output, Pystache's template rendering methods return only unicode.

Pystache's Renderer class supports a number of attributes to control how Pystache converts byte strings to unicode on input. These include the file_encoding, string_encoding, and decode_errors attributes.

The file_encoding attribute is the encoding the renderer uses to convert to unicode any files read from the file system. Similarly, string_encoding is the encoding the renderer uses to convert any other byte strings encountered during the rendering process into unicode (e.g. context values that are encoded byte strings).

The decode_errors attribute is what the renderer passes as the errors argument to Python's built-in unicode-decoding function (str() in Python 3 and unicode() in Python 2). The valid values for this argument are strict, ignore, and replace.

Each of these attributes can be set via the Renderer class's constructor using a keyword argument of the same name. See the Renderer class's docstrings for further details. In addition, the file_encoding attribute can be controlled on a per-view basis by subclassing the TemplateSpec class. When not specified explicitly, these attributes default to values set in Pystache's defaults module.

Develop

To test from a source distribution (without installing)--

python test_pystache.py

To test Pystache with multiple versions of Python (with a single command!), you can use tox:

pip install 'virtualenv<1.8'  # Version 1.8 dropped support for Python 2.4.
pip install 'tox<1.4'  # Version 1.4 dropped support for Python 2.4.
tox

If you do not have all Python versions listed in tox.ini--

tox -e py26,py32  # for example

The source distribution tests also include doctests and tests from the Mustache spec. To include tests from the Mustache spec in your test runs:

git submodule init
git submodule update

The test harness parses the spec's (more human-readable) yaml files if PyYAML is present. Otherwise, it parses the json files. To install PyYAML--

pip install pyyaml

To run a subset of the tests, you can use nose:

pip install nose
nosetests --tests pystache/tests/test_context.py:GetValueTests.test_dictionary__key_present

Using Python 3 with Pystache from source

Pystache is written in Python 2 and must be converted to Python 3 prior to using it with Python 3. The installation process (and tox) do this automatically.

To convert the code to Python 3 manually (while using Python 3)--

python setup.py build

This writes the converted code to a subdirectory called build. By design, Python 3 builds cannot be created from Python 2.

To convert the code without using setup.py, you can use 2to3 as follows (two steps)--

2to3 --write --nobackups --no-diffs --doctests_only pystache
2to3 --write --nobackups --no-diffs pystache

This converts the code (and doctests) in place.

To import pystache from a source distribution while using Python 3, be sure that you are importing from a directory containing a converted version of the code (e.g. from the build directory after converting), and not from the original (unconverted) source directory. Otherwise, you will get a syntax error. You can help prevent this by not running the Python IDE from the project directory when importing Pystache while using Python 3.

Mailing List

There is a mailing list. Note that there is a bit of a delay between posting a message and seeing it appear in the mailing list archive.

Credits

>>> context = { 'author': 'Chris Wanstrath', 'maintainer': 'Chris Jerdonek' }
>>> print pystache.render("Author: {{author}}\nMaintainer: {{maintainer}}", context)
Author: Chris Wanstrath
Maintainer: Chris Jerdonek

Pystache logo by David Phillips is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License.