# coding: utf-8 """ This module provides a Renderer class to render templates. """ import sys from pystache import defaults from pystache.common import TemplateNotFoundError from pystache.context import ContextStack from pystache.loader import Loader from pystache.renderengine import RenderEngine from pystache.specloader import SpecLoader from pystache.template_spec import TemplateSpec # TODO: come up with a better solution for this. One of the issues here # is that in Python 3 there is no common base class for unicode strings # and byte strings, and 2to3 seems to convert all of "str", "unicode", # and "basestring" to Python 3's "str". if sys.version_info < (3, ): _STRING_TYPES = basestring else: # The latter evaluates to "bytes" in Python 3 -- even after conversion by 2to3. _STRING_TYPES = (unicode, type(u"a".encode('utf-8'))) class Renderer(object): """ A class for rendering mustache templates. This class supports several rendering options which are described in the constructor's docstring. Among these, the constructor supports passing a custom partial loader. Here is an example of rendering a template using a custom partial loader that loads partials from a string-string dictionary. >>> partials = {'partial': 'Hello, {{thing}}!'} >>> renderer = Renderer(partials=partials) >>> # We apply print to make the test work in Python 3 after 2to3. >>> print renderer.render('{{>partial}}', {'thing': 'world'}) Hello, world! """ def __init__(self, file_encoding=None, string_encoding=None, decode_errors=None, search_dirs=None, file_extension=None, escape=None, partials=None): """ Construct an instance. Arguments: partials: an object (e.g. a dictionary) for custom partial loading during the rendering process. The object should have a get() method that accepts a string and returns the corresponding template as a string, preferably as a unicode string. If there is no template with that name, the get() method should either return None (as dict.get() does) or raise an exception. If this argument is None, the rendering process will use the normal procedure of locating and reading templates from the file system -- using relevant instance attributes like search_dirs, file_encoding, etc. decode_errors: the string to pass as the errors argument to the built-in function unicode() when converting str strings to unicode. Defaults to the package default. escape: the function used to escape variable tag values when rendering a template. The function should accept a unicode string (or subclass of unicode) and return an escaped string that is again unicode (or a subclass of unicode). This function need not handle strings of type `str` because this class will only pass it unicode strings. The constructor assigns this function to the constructed instance's escape() method. To disable escaping entirely, one can pass `lambda u: u` as the escape function, for example. One may also wish to consider using markupsafe's escape function: markupsafe.escape(). This argument defaults to the package default. file_encoding: the name of the default encoding to use when reading template files. All templates are converted to unicode prior to parsing. This encoding is used when reading template files and converting them to unicode. Defaults to the package default. file_extension: the template file extension. Pass False for no extension (i.e. to use extensionless template files). Defaults to the package default. search_dirs: the list of directories in which to search when loading a template by name or file name. If given a string, the method interprets the string as a single directory. Defaults to the package default. string_encoding: the name of the encoding to use when converting to unicode any strings of type str encountered during the rendering process. The name will be passed as the encoding argument to the built-in function unicode(). Defaults to the package default. """ if decode_errors is None: decode_errors = defaults.DECODE_ERRORS if escape is None: escape = defaults.TAG_ESCAPE if file_encoding is None: file_encoding = defaults.FILE_ENCODING if file_extension is None: file_extension = defaults.TEMPLATE_EXTENSION if search_dirs is None: search_dirs = defaults.SEARCH_DIRS if string_encoding is None: string_encoding = defaults.STRING_ENCODING if isinstance(search_dirs, basestring): search_dirs = [search_dirs] self._context = None self.decode_errors = decode_errors self.escape = escape self.file_encoding = file_encoding self.file_extension = file_extension self.partials = partials self.search_dirs = search_dirs self.string_encoding = string_encoding # This is an experimental way of giving views access to the current context. # TODO: consider another approach of not giving access via a property, # but instead letting the caller pass the initial context to the # main render() method by reference. This approach would probably # be less likely to be misused. @property def context(self): """ Return the current rendering context [experimental]. """ return self._context def _to_unicode_soft(self, s): """ Convert a basestring to unicode, preserving any unicode subclass. """ # We type-check to avoid "TypeError: decoding Unicode is not supported". # We avoid the Python ternary operator for Python 2.4 support. if isinstance(s, unicode): return s return self.unicode(s) def _to_unicode_hard(self, s): """ Convert a basestring to a string with type unicode (not subclass). """ return unicode(self._to_unicode_soft(s)) def _escape_to_unicode(self, s): """ Convert a basestring to unicode (preserving any unicode subclass), and escape it. Returns a unicode string (not subclass). """ return unicode(self.escape(self._to_unicode_soft(s))) def unicode(self, b, encoding=None): """ Convert a byte string to unicode, using string_encoding and decode_errors. Arguments: b: a byte string. encoding: the name of an encoding. Defaults to the string_encoding attribute for this instance. Raises: TypeError: Because this method calls Python's built-in unicode() function, this method raises the following exception if the given string is already unicode: TypeError: decoding Unicode is not supported """ if encoding is None: encoding = self.string_encoding # TODO: Wrap UnicodeDecodeErrors with a message about setting # the string_encoding and decode_errors attributes. return unicode(b, encoding, self.decode_errors) def _make_loader(self): """ Create a Loader instance using current attributes. """ return Loader(file_encoding=self.file_encoding, extension=self.file_extension, to_unicode=self.unicode, search_dirs=self.search_dirs) def _make_load_template(self): """ Return a function that loads a template by name. """ loader = self._make_loader() def load_template(template_name): return loader.load_name(template_name) return load_template def _make_load_partial(self): """ Return the load_partial function to pass to RenderEngine.__init__(). """ if self.partials is None: load_template = self._make_load_template() return load_template # Otherwise, create a load_partial function from the custom partial # loader that satisfies RenderEngine requirements (and that provides # a nicer exception, etc). partials = self.partials def load_partial(name): template = partials.get(name) if template is None: raise TemplateNotFoundError("Name %s not found in partials: %s" % (repr(name), type(partials))) # RenderEngine requires that the return value be unicode. return self._to_unicode_hard(template) return load_partial def _make_render_engine(self): """ Return a RenderEngine instance for rendering. """ load_partial = self._make_load_partial() engine = RenderEngine(load_partial=load_partial, literal=self._to_unicode_hard, escape=self._escape_to_unicode) return engine # TODO: add unit tests for this method. def load_template(self, template_name): """ Load a template by name from the file system. """ load_template = self._make_load_template() return load_template(template_name) def _render_string(self, template, *context, **kwargs): """ Render the given template string using the given context. """ # RenderEngine.render() requires that the template string be unicode. template = self._to_unicode_hard(template) context = ContextStack.create(*context, **kwargs) self._context = context engine = self._make_render_engine() rendered = engine.render(template, context) return unicode(rendered) def _render_object(self, obj, *context, **kwargs): """ Render the template associated with the given object. """ loader = self._make_loader() # TODO: consider an approach that does not require using an if # block here. For example, perhaps this class's loader can be # a SpecLoader in all cases, and the SpecLoader instance can # check the object's type. Or perhaps Loader and SpecLoader # can be refactored to implement the same interface. if isinstance(obj, TemplateSpec): loader = SpecLoader(loader) template = loader.load(obj) else: template = loader.load_object(obj) context = [obj] + list(context) return self._render_string(template, *context, **kwargs) def render_path(self, template_path, *context, **kwargs): """ Render the template at the given path using the given context. Read the render() docstring for more information. """ loader = self._make_loader() template = loader.read(template_path) return self._render_string(template, *context, **kwargs) def render(self, template, *context, **kwargs): """ Render the given template (or template object) using the given context. Returns the rendering as a unicode string. Prior to rendering, templates of type str are converted to unicode using the string_encoding and decode_errors attributes. See the constructor docstring for more information. Arguments: template: a template string of type unicode or str, or an object instance. If the argument is an object, the function first looks for the template associated to the object by calling this class's get_associated_template() method. The rendering process also uses the passed object as the first element of the context stack when rendering. *context: zero or more dictionaries, ContextStack instances, or objects with which to populate the initial context stack. None arguments are skipped. Items in the *context list are added to the context stack in order so that later items in the argument list take precedence over earlier items. **kwargs: additional key-value data to add to the context stack. As these arguments appear after all items in the *context list, in the case of key conflicts these values take precedence over all items in the *context list. """ if isinstance(template, _STRING_TYPES): return self._render_string(template, *context, **kwargs) # Otherwise, we assume the template is an object. return self._render_object(template, *context, **kwargs)