Add Python templating engine Jinja2 to third_party

third_party/jinja2/environment.py

Index: third_party/jinja2/environment.py
diff --git a/third_party/jinja2/environment.py b/third_party/jinja2/environment.py
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+# -*- coding: utf-8 -*-
+"""
+    jinja2.environment
+    ~~~~~~~~~~~~~~~~~~
+
+    Provides a class that holds runtime and parsing time options.
+
+    :copyright: (c) 2010 by the Jinja Team.
+    :license: BSD, see LICENSE for more details.
+"""
+import os
+import sys
+from jinja2 import nodes
+from jinja2.defaults import *
+from jinja2.lexer import get_lexer, TokenStream
+from jinja2.parser import Parser
+from jinja2.optimizer import optimize
+from jinja2.compiler import generate
+from jinja2.runtime import Undefined, new_context
+from jinja2.exceptions import TemplateSyntaxError, TemplateNotFound, \
+     TemplatesNotFound
+from jinja2.utils import import_string, LRUCache, Markup, missing, \
+     concat, consume, internalcode, _encode_filename
+
+
+# for direct template usage we have up to ten living environments
+_spontaneous_environments = LRUCache(10)
+
+# the function to create jinja traceback objects.  This is dynamically
+# imported on the first exception in the exception handler.
+_make_traceback = None
+
+
+def get_spontaneous_environment(*args):
+    """Return a new spontaneous environment.  A spontaneous environment is an
+    unnamed and unaccessible (in theory) environment that is used for
+    templates generated from a string and not from the file system.
+    """
+    try:
+        env = _spontaneous_environments.get(args)
+    except TypeError:
+        return Environment(*args)
+    if env is not None:
+        return env
+    _spontaneous_environments[args] = env = Environment(*args)
+    env.shared = True
+    return env
+
+
+def create_cache(size):
+    """Return the cache class for the given size."""
+    if size == 0:
+        return None
+    if size < 0:
+        return {}
+    return LRUCache(size)
+
+
+def copy_cache(cache):
+    """Create an empty copy of the given cache."""
+    if cache is None:
+        return None
+    elif type(cache) is dict:
+        return {}
+    return LRUCache(cache.capacity)
+
+
+def load_extensions(environment, extensions):
+    """Load the extensions from the list and bind it to the environment.
+    Returns a dict of instanciated environments.
+    """
+    result = {}
+    for extension in extensions:
+        if isinstance(extension, basestring):
+            extension = import_string(extension)
+        result[extension.identifier] = extension(environment)
+    return result
+
+
+def _environment_sanity_check(environment):
+    """Perform a sanity check on the environment."""
+    assert issubclass(environment.undefined, Undefined), 'undefined must ' \
+           'be a subclass of undefined because filters depend on it.'
+    assert environment.block_start_string != \
+           environment.variable_start_string != \
+           environment.comment_start_string, 'block, variable and comment ' \
+           'start strings must be different'
+    assert environment.newline_sequence in ('\r', '\r\n', '\n'), \
+           'newline_sequence set to unknown line ending string.'
+    return environment
+
+
+class Environment(object):
+    r"""The core component of Jinja is the `Environment`.  It contains
+    important shared variables like configuration, filters, tests,
+    globals and others.  Instances of this class may be modified if
+    they are not shared and if no template was loaded so far.
+    Modifications on environments after the first template was loaded
+    will lead to surprising effects and undefined behavior.
+
+    Here the possible initialization parameters:
+
+        `block_start_string`
+            The string marking the begin of a block.  Defaults to ``'{%'``.
+
+        `block_end_string`
+            The string marking the end of a block.  Defaults to ``'%}'``.
+
+        `variable_start_string`
+            The string marking the begin of a print statement.
+            Defaults to ``'{{'``.
+
+        `variable_end_string`
+            The string marking the end of a print statement.  Defaults to
+            ``'}}'``.
+
+        `comment_start_string`
+            The string marking the begin of a comment.  Defaults to ``'{#'``.
+
+        `comment_end_string`
+            The string marking the end of a comment.  Defaults to ``'#}'``.
+
+        `line_statement_prefix`
+            If given and a string, this will be used as prefix for line based
+            statements.  See also :ref:`line-statements`.
+
+        `line_comment_prefix`
+            If given and a string, this will be used as prefix for line based
+            based comments.  See also :ref:`line-statements`.
+
+            .. versionadded:: 2.2
+
+        `trim_blocks`
+            If this is set to ``True`` the first newline after a block is
+            removed (block, not variable tag!).  Defaults to `False`.
+
+        `newline_sequence`
+            The sequence that starts a newline.  Must be one of ``'\r'``,
+            ``'\n'`` or ``'\r\n'``.  The default is ``'\n'`` which is a
+            useful default for Linux and OS X systems as well as web
+            applications.
+
+        `extensions`
+            List of Jinja extensions to use.  This can either be import paths
+            as strings or extension classes.  For more information have a
+            look at :ref:`the extensions documentation <jinja-extensions>`.
+
+        `optimized`
+            should the optimizer be enabled?  Default is `True`.
+
+        `undefined`
+            :class:`Undefined` or a subclass of it that is used to represent
+            undefined values in the template.
+
+        `finalize`
+            A callable that can be used to process the result of a variable
+            expression before it is output.  For example one can convert
+            `None` implicitly into an empty string here.
+
+        `autoescape`
+            If set to true the XML/HTML autoescaping feature is enabled by
+            default.  For more details about auto escaping see
+            :class:`~jinja2.utils.Markup`.  As of Jinja 2.4 this can also
+            be a callable that is passed the template name and has to
+            return `True` or `False` depending on autoescape should be
+            enabled by default.
+
+            .. versionchanged:: 2.4
+               `autoescape` can now be a function
+
+        `loader`
+            The template loader for this environment.
+
+        `cache_size`
+            The size of the cache.  Per default this is ``50`` which means
+            that if more than 50 templates are loaded the loader will clean
+            out the least recently used template.  If the cache size is set to
+            ``0`` templates are recompiled all the time, if the cache size is
+            ``-1`` the cache will not be cleaned.
+
+        `auto_reload`
+            Some loaders load templates from locations where the template
+            sources may change (ie: file system or database).  If
+            `auto_reload` is set to `True` (default) every time a template is
+            requested the loader checks if the source changed and if yes, it
+            will reload the template.  For higher performance it's possible to
+            disable that.
+
+        `bytecode_cache`
+            If set to a bytecode cache object, this object will provide a
+            cache for the internal Jinja bytecode so that templates don't
+            have to be parsed if they were not changed.
+
+            See :ref:`bytecode-cache` for more information.
+    """
+
+    #: if this environment is sandboxed.  Modifying this variable won't make
+    #: the environment sandboxed though.  For a real sandboxed environment
+    #: have a look at jinja2.sandbox.  This flag alone controls the code
+    #: generation by the compiler.
+    sandboxed = False
+
+    #: True if the environment is just an overlay
+    overlayed = False
+
+    #: the environment this environment is linked to if it is an overlay
+    linked_to = None
+
+    #: shared environments have this set to `True`.  A shared environment
+    #: must not be modified
+    shared = False
+
+    #: these are currently EXPERIMENTAL undocumented features.
+    exception_handler = None
+    exception_formatter = None
+
+    def __init__(self,
+                 block_start_string=BLOCK_START_STRING,
+                 block_end_string=BLOCK_END_STRING,
+                 variable_start_string=VARIABLE_START_STRING,
+                 variable_end_string=VARIABLE_END_STRING,
+                 comment_start_string=COMMENT_START_STRING,
+                 comment_end_string=COMMENT_END_STRING,
+                 line_statement_prefix=LINE_STATEMENT_PREFIX,
+                 line_comment_prefix=LINE_COMMENT_PREFIX,
+                 trim_blocks=TRIM_BLOCKS,
+                 newline_sequence=NEWLINE_SEQUENCE,
+                 extensions=(),
+                 optimized=True,
+                 undefined=Undefined,
+                 finalize=None,
+                 autoescape=False,
+                 loader=None,
+                 cache_size=50,
+                 auto_reload=True,
+                 bytecode_cache=None):
+        # !!Important notice!!
+        #   The constructor accepts quite a few arguments that should be
+        #   passed by keyword rather than position.  However it's important to
+        #   not change the order of arguments because it's used at least
+        #   internally in those cases:
+        #       -   spontaneus environments (i18n extension and Template)
+        #       -   unittests
+        #   If parameter changes are required only add parameters at the end
+        #   and don't change the arguments (or the defaults!) of the arguments
+        #   existing already.
+
+        # lexer / parser information
+        self.block_start_string = block_start_string
+        self.block_end_string = block_end_string
+        self.variable_start_string = variable_start_string
+        self.variable_end_string = variable_end_string
+        self.comment_start_string = comment_start_string
+        self.comment_end_string = comment_end_string
+        self.line_statement_prefix = line_statement_prefix
+        self.line_comment_prefix = line_comment_prefix
+        self.trim_blocks = trim_blocks
+        self.newline_sequence = newline_sequence
+
+        # runtime information
+        self.undefined = undefined
+        self.optimized = optimized
+        self.finalize = finalize
+        self.autoescape = autoescape
+
+        # defaults
+        self.filters = DEFAULT_FILTERS.copy()
+        self.tests = DEFAULT_TESTS.copy()
+        self.globals = DEFAULT_NAMESPACE.copy()
+
+        # set the loader provided
+        self.loader = loader
+        self.bytecode_cache = None
+        self.cache = create_cache(cache_size)
+        self.bytecode_cache = bytecode_cache
+        self.auto_reload = auto_reload
+
+        # load extensions
+        self.extensions = load_extensions(self, extensions)
+
+        _environment_sanity_check(self)
+
+    def add_extension(self, extension):
+        """Adds an extension after the environment was created.
+
+        .. versionadded:: 2.5
+        """
+        self.extensions.update(load_extensions(self, [extension]))
+
+    def extend(self, **attributes):
+        """Add the items to the instance of the environment if they do not exist
+        yet.  This is used by :ref:`extensions <writing-extensions>` to register
+        callbacks and configuration values without breaking inheritance.
+        """
+        for key, value in attributes.iteritems():
+            if not hasattr(self, key):
+                setattr(self, key, value)
+
+    def overlay(self, block_start_string=missing, block_end_string=missing,
+                variable_start_string=missing, variable_end_string=missing,
+                comment_start_string=missing, comment_end_string=missing,
+                line_statement_prefix=missing, line_comment_prefix=missing,
+                trim_blocks=missing, extensions=missing, optimized=missing,
+                undefined=missing, finalize=missing, autoescape=missing,
+                loader=missing, cache_size=missing, auto_reload=missing,
+                bytecode_cache=missing):
+        """Create a new overlay environment that shares all the data with the
+        current environment except of cache and the overridden attributes.
+        Extensions cannot be removed for an overlayed environment.  An overlayed
+        environment automatically gets all the extensions of the environment it
+        is linked to plus optional extra extensions.
+
+        Creating overlays should happen after the initial environment was set
+        up completely.  Not all attributes are truly linked, some are just
+        copied over so modifications on the original environment may not shine
+        through.
+        """
+        args = dict(locals())
+        del args['self'], args['cache_size'], args['extensions']
+
+        rv = object.__new__(self.__class__)
+        rv.__dict__.update(self.__dict__)
+        rv.overlayed = True
+        rv.linked_to = self
+
+        for key, value in args.iteritems():
+            if value is not missing:
+                setattr(rv, key, value)
+
+        if cache_size is not missing:
+            rv.cache = create_cache(cache_size)
+        else:
+            rv.cache = copy_cache(self.cache)
+
+        rv.extensions = {}
+        for key, value in self.extensions.iteritems():
+            rv.extensions[key] = value.bind(rv)
+        if extensions is not missing:
+            rv.extensions.update(load_extensions(rv, extensions))
+
+        return _environment_sanity_check(rv)
+
+    lexer = property(get_lexer, doc="The lexer for this environment.")
+
+    def iter_extensions(self):
+        """Iterates over the extensions by priority."""
+        return iter(sorted(self.extensions.values(),
+                           key=lambda x: x.priority))
+
+    def getitem(self, obj, argument):
+        """Get an item or attribute of an object but prefer the item."""
+        try:
+            return obj[argument]
+        except (TypeError, LookupError):
+            if isinstance(argument, basestring):
+                try:
+                    attr = str(argument)
+                except Exception:
+                    pass
+                else:
+                    try:
+                        return getattr(obj, attr)
+                    except AttributeError:
+                        pass
+            return self.undefined(obj=obj, name=argument)
+
+    def getattr(self, obj, attribute):
+        """Get an item or attribute of an object but prefer the attribute.
+        Unlike :meth:`getitem` the attribute *must* be a bytestring.
+        """
+        try:
+            return getattr(obj, attribute)
+        except AttributeError:
+            pass
+        try:
+            return obj[attribute]
+        except (TypeError, LookupError, AttributeError):
+            return self.undefined(obj=obj, name=attribute)
+
+    @internalcode
+    def parse(self, source, name=None, filename=None):
+        """Parse the sourcecode and return the abstract syntax tree.  This
+        tree of nodes is used by the compiler to convert the template into
+        executable source- or bytecode.  This is useful for debugging or to
+        extract information from templates.
+
+        If you are :ref:`developing Jinja2 extensions <writing-extensions>`
+        this gives you a good overview of the node tree generated.
+        """
+        try:
+            return self._parse(source, name, filename)
+        except TemplateSyntaxError:
+            exc_info = sys.exc_info()
+        self.handle_exception(exc_info, source_hint=source)
+
+    def _parse(self, source, name, filename):
+        """Internal parsing function used by `parse` and `compile`."""
+        return Parser(self, source, name, _encode_filename(filename)).parse()
+
+    def lex(self, source, name=None, filename=None):
+        """Lex the given sourcecode and return a generator that yields
+        tokens as tuples in the form ``(lineno, token_type, value)``.
+        This can be useful for :ref:`extension development <writing-extensions>`
+        and debugging templates.
+
+        This does not perform preprocessing.  If you want the preprocessing
+        of the extensions to be applied you have to filter source through
+        the :meth:`preprocess` method.
+        """
+        source = unicode(source)
+        try:
+            return self.lexer.tokeniter(source, name, filename)
+        except TemplateSyntaxError:
+            exc_info = sys.exc_info()
+        self.handle_exception(exc_info, source_hint=source)
+
+    def preprocess(self, source, name=None, filename=None):
+        """Preprocesses the source with all extensions.  This is automatically
+        called for all parsing and compiling methods but *not* for :meth:`lex`
+        because there you usually only want the actual source tokenized.
+        """
+        return reduce(lambda s, e: e.preprocess(s, name, filename),
+                      self.iter_extensions(), unicode(source))
+
+    def _tokenize(self, source, name, filename=None, state=None):
+        """Called by the parser to do the preprocessing and filtering
+        for all the extensions.  Returns a :class:`~jinja2.lexer.TokenStream`.
+        """
+        source = self.preprocess(source, name, filename)
+        stream = self.lexer.tokenize(source, name, filename, state)
+        for ext in self.iter_extensions():
+            stream = ext.filter_stream(stream)
+            if not isinstance(stream, TokenStream):
+                stream = TokenStream(stream, name, filename)
+        return stream
+
+    def _generate(self, source, name, filename, defer_init=False):
+        """Internal hook that can be overriden to hook a different generate
+        method in.
+
+        .. versionadded:: 2.5
+        """
+        return generate(source, self, name, filename, defer_init=defer_init)
+
+    def _compile(self, source, filename):
+        """Internal hook that can be overriden to hook a different compile
+        method in.
+
+        .. versionadded:: 2.5
+        """
+        return compile(source, filename, 'exec')
+
+    @internalcode
+    def compile(self, source, name=None, filename=None, raw=False,
+                defer_init=False):
+        """Compile a node or template source code.  The `name` parameter is
+        the load name of the template after it was joined using
+        :meth:`join_path` if necessary, not the filename on the file system.
+        the `filename` parameter is the estimated filename of the template on
+        the file system.  If the template came from a database or memory this
+        can be omitted.
+
+        The return value of this method is a python code object.  If the `raw`
+        parameter is `True` the return value will be a string with python
+        code equivalent to the bytecode returned otherwise.  This method is
+        mainly used internally.
+
+        `defer_init` is use internally to aid the module code generator.  This
+        causes the generated code to be able to import without the global
+        environment variable to be set.
+
+        .. versionadded:: 2.4
+           `defer_init` parameter added.
+        """
+        source_hint = None
+        try:
+            if isinstance(source, basestring):
+                source_hint = source
+                source = self._parse(source, name, filename)
+            if self.optimized:
+                source = optimize(source, self)
+            source = self._generate(source, name, filename,
+                                    defer_init=defer_init)
+            if raw:
+                return source
+            if filename is None:
+                filename = '<template>'
+            else:
+                filename = _encode_filename(filename)
+            return self._compile(source, filename)
+        except TemplateSyntaxError:
+            exc_info = sys.exc_info()
+        self.handle_exception(exc_info, source_hint=source)
+
+    def compile_expression(self, source, undefined_to_none=True):
+        """A handy helper method that returns a callable that accepts keyword
+        arguments that appear as variables in the expression.  If called it
+        returns the result of the expression.
+
+        This is useful if applications want to use the same rules as Jinja
+        in template "configuration files" or similar situations.
+
+        Example usage:
+
+        >>> env = Environment()
+        >>> expr = env.compile_expression('foo == 42')
+        >>> expr(foo=23)
+        False
+        >>> expr(foo=42)
+        True
+
+        Per default the return value is converted to `None` if the
+        expression returns an undefined value.  This can be changed
+        by setting `undefined_to_none` to `False`.
+
+        >>> env.compile_expression('var')() is None
+        True
+        >>> env.compile_expression('var', undefined_to_none=False)()
+        Undefined
+
+        .. versionadded:: 2.1
+        """
+        parser = Parser(self, source, state='variable')
+        exc_info = None
+        try:
+            expr = parser.parse_expression()
+            if not parser.stream.eos:
+                raise TemplateSyntaxError('chunk after expression',
+                                          parser.stream.current.lineno,
+                                          None, None)
+            expr.set_environment(self)
+        except TemplateSyntaxError:
+            exc_info = sys.exc_info()
+        if exc_info is not None:
+            self.handle_exception(exc_info, source_hint=source)
+        body = [nodes.Assign(nodes.Name('result', 'store'), expr, lineno=1)]
+        template = self.from_string(nodes.Template(body, lineno=1))
+        return TemplateExpression(template, undefined_to_none)
+
+    def compile_templates(self, target, extensions=None, filter_func=None,
+                          zip='deflated', log_function=None,
+                          ignore_errors=True, py_compile=False):
+        """Finds all the templates the loader can find, compiles them
+        and stores them in `target`.  If `zip` is `None`, instead of in a
+        zipfile, the templates will be will be stored in a directory.
+        By default a deflate zip algorithm is used, to switch to
+        the stored algorithm, `zip` can be set to ``'stored'``.
+
+        `extensions` and `filter_func` are passed to :meth:`list_templates`.
+        Each template returned will be compiled to the target folder or
+        zipfile.
+
+        By default template compilation errors are ignored.  In case a
+        log function is provided, errors are logged.  If you want template
+        syntax errors to abort the compilation you can set `ignore_errors`
+        to `False` and you will get an exception on syntax errors.
+
+        If `py_compile` is set to `True` .pyc files will be written to the
+        target instead of standard .py files.
+
+        .. versionadded:: 2.4
+        """
+        from jinja2.loaders import ModuleLoader
+
+        if log_function is None:
+            log_function = lambda x: None
+
+        if py_compile:
+            import imp, marshal
+            py_header = imp.get_magic() + \
+                u'\xff\xff\xff\xff'.encode('iso-8859-15')
+
+        def write_file(filename, data, mode):
+            if zip:
+                info = ZipInfo(filename)
+                info.external_attr = 0755 << 16L
+                zip_file.writestr(info, data)
+            else:
+                f = open(os.path.join(target, filename), mode)
+                try:
+                    f.write(data)
+                finally:
+                    f.close()
+
+        if zip is not None:
+            from zipfile import ZipFile, ZipInfo, ZIP_DEFLATED, ZIP_STORED
+            zip_file = ZipFile(target, 'w', dict(deflated=ZIP_DEFLATED,
+                                                 stored=ZIP_STORED)[zip])
+            log_function('Compiling into Zip archive "%s"' % target)
+        else:
+            if not os.path.isdir(target):
+                os.makedirs(target)
+            log_function('Compiling into folder "%s"' % target)
+
+        try:
+            for name in self.list_templates(extensions, filter_func):
+                source, filename, _ = self.loader.get_source(self, name)
+                try:
+                    code = self.compile(source, name, filename, True, True)
+                except TemplateSyntaxError, e:
+                    if not ignore_errors:
+                        raise
+                    log_function('Could not compile "%s": %s' % (name, e))
+                    continue
+
+                filename = ModuleLoader.get_module_filename(name)
+
+                if py_compile:
+                    c = self._compile(code, _encode_filename(filename))
+                    write_file(filename + 'c', py_header +
+                               marshal.dumps(c), 'wb')
+                    log_function('Byte-compiled "%s" as %s' %
+                                 (name, filename + 'c'))
+                else:
+                    write_file(filename, code, 'w')
+                    log_function('Compiled "%s" as %s' % (name, filename))
+        finally:
+            if zip:
+                zip_file.close()
+
+        log_function('Finished compiling templates')
+
+    def list_templates(self, extensions=None, filter_func=None):
+        """Returns a list of templates for this environment.  This requires
+        that the loader supports the loader's
+        :meth:`~BaseLoader.list_templates` method.
+
+        If there are other files in the template folder besides the
+        actual templates, the returned list can be filtered.  There are two
+        ways: either `extensions` is set to a list of file extensions for
+        templates, or a `filter_func` can be provided which is a callable that
+        is passed a template name and should return `True` if it should end up
+        in the result list.
+
+        If the loader does not support that, a :exc:`TypeError` is raised.
+
+        .. versionadded:: 2.4
+        """
+        x = self.loader.list_templates()
+        if extensions is not None:
+            if filter_func is not None:
+                raise TypeError('either extensions or filter_func '
+                                'can be passed, but not both')
+            filter_func = lambda x: '.' in x and \
+                                    x.rsplit('.', 1)[1] in extensions
+        if filter_func is not None:
+            x = filter(filter_func, x)
+        return x
+
+    def handle_exception(self, exc_info=None, rendered=False, source_hint=None):
+        """Exception handling helper.  This is used internally to either raise
+        rewritten exceptions or return a rendered traceback for the template.
+        """
+        global _make_traceback
+        if exc_info is None:
+            exc_info = sys.exc_info()
+
+        # the debugging module is imported when it's used for the first time.
+        # we're doing a lot of stuff there and for applications that do not
+        # get any exceptions in template rendering there is no need to load
+        # all of that.
+        if _make_traceback is None:
+            from jinja2.debug import make_traceback as _make_traceback
+        traceback = _make_traceback(exc_info, source_hint)
+        if rendered and self.exception_formatter is not None:
+            return self.exception_formatter(traceback)
+        if self.exception_handler is not None:
+            self.exception_handler(traceback)
+        exc_type, exc_value, tb = traceback.standard_exc_info
+        raise exc_type, exc_value, tb
+
+    def join_path(self, template, parent):
+        """Join a template with the parent.  By default all the lookups are
+        relative to the loader root so this method returns the `template`
+        parameter unchanged, but if the paths should be relative to the
+        parent template, this function can be used to calculate the real
+        template name.
+
+        Subclasses may override this method and implement template path
+        joining here.
+        """
+        return template
+
+    @internalcode
+    def _load_template(self, name, globals):
+        if self.loader is None:
+            raise TypeError('no loader for this environment specified')
+        if self.cache is not None:
+            template = self.cache.get(name)
+            if template is not None and (not self.auto_reload or \
+                                         template.is_up_to_date):
+                return template
+        template = self.loader.load(self, name, globals)
+        if self.cache is not None:
+            self.cache[name] = template
+        return template
+
+    @internalcode
+    def get_template(self, name, parent=None, globals=None):
+        """Load a template from the loader.  If a loader is configured this
+        method ask the loader for the template and returns a :class:`Template`.
+        If the `parent` parameter is not `None`, :meth:`join_path` is called
+        to get the real template name before loading.
+
+        The `globals` parameter can be used to provide template wide globals.
+        These variables are available in the context at render time.
+
+        If the template does not exist a :exc:`TemplateNotFound` exception is
+        raised.
+
+        .. versionchanged:: 2.4
+           If `name` is a :class:`Template` object it is returned from the
+           function unchanged.
+        """
+        if isinstance(name, Template):
+            return name
+        if parent is not None:
+            name = self.join_path(name, parent)
+        return self._load_template(name, self.make_globals(globals))
+
+    @internalcode
+    def select_template(self, names, parent=None, globals=None):
+        """Works like :meth:`get_template` but tries a number of templates
+        before it fails.  If it cannot find any of the templates, it will
+        raise a :exc:`TemplatesNotFound` exception.
+
+        .. versionadded:: 2.3
+
+        .. versionchanged:: 2.4
+           If `names` contains a :class:`Template` object it is returned
+           from the function unchanged.
+        """
+        if not names:
+            raise TemplatesNotFound(message=u'Tried to select from an empty list '
+                                            u'of templates.')
+        globals = self.make_globals(globals)
+        for name in names:
+            if isinstance(name, Template):
+                return name
+            if parent is not None:
+                name = self.join_path(name, parent)
+            try:
+                return self._load_template(name, globals)
+            except TemplateNotFound:
+                pass
+        raise TemplatesNotFound(names)
+
+    @internalcode
+    def get_or_select_template(self, template_name_or_list,
+                               parent=None, globals=None):
+        """Does a typecheck and dispatches to :meth:`select_template`
+        if an iterable of template names is given, otherwise to
+        :meth:`get_template`.
+
+        .. versionadded:: 2.3
+        """
+        if isinstance(template_name_or_list, basestring):
+            return self.get_template(template_name_or_list, parent, globals)
+        elif isinstance(template_name_or_list, Template):
+            return template_name_or_list
+        return self.select_template(template_name_or_list, parent, globals)
+
+    def from_string(self, source, globals=None, template_class=None):
+        """Load a template from a string.  This parses the source given and
+        returns a :class:`Template` object.
+        """
+        globals = self.make_globals(globals)
+        cls = template_class or self.template_class
+        return cls.from_code(self, self.compile(source), globals, None)
+
+    def make_globals(self, d):
+        """Return a dict for the globals."""
+        if not d:
+            return self.globals
+        return dict(self.globals, **d)
+
+
+class Template(object):
+    """The central template object.  This class represents a compiled template
+    and is used to evaluate it.
+
+    Normally the template object is generated from an :class:`Environment` but
+    it also has a constructor that makes it possible to create a template
+    instance directly using the constructor.  It takes the same arguments as
+    the environment constructor but it's not possible to specify a loader.
+
+    Every template object has a few methods and members that are guaranteed
+    to exist.  However it's important that a template object should be
+    considered immutable.  Modifications on the object are not supported.
+
+    Template objects created from the constructor rather than an environment
+    do have an `environment` attribute that points to a temporary environment
+    that is probably shared with other templates created with the constructor
+    and compatible settings.
+
+    >>> template = Template('Hello {{ name }}!')
+    >>> template.render(name='John Doe')
+    u'Hello John Doe!'
+
+    >>> stream = template.stream(name='John Doe')
+    >>> stream.next()
+    u'Hello John Doe!'
+    >>> stream.next()
+    Traceback (most recent call last):
+        ...
+    StopIteration
+    """
+
+    def __new__(cls, source,
+                block_start_string=BLOCK_START_STRING,
+                block_end_string=BLOCK_END_STRING,
+                variable_start_string=VARIABLE_START_STRING,
+                variable_end_string=VARIABLE_END_STRING,
+                comment_start_string=COMMENT_START_STRING,
+                comment_end_string=COMMENT_END_STRING,
+                line_statement_prefix=LINE_STATEMENT_PREFIX,
+                line_comment_prefix=LINE_COMMENT_PREFIX,
+                trim_blocks=TRIM_BLOCKS,
+                newline_sequence=NEWLINE_SEQUENCE,
+                extensions=(),
+                optimized=True,
+                undefined=Undefined,
+                finalize=None,
+                autoescape=False):
+        env = get_spontaneous_environment(
+            block_start_string, block_end_string, variable_start_string,
+            variable_end_string, comment_start_string, comment_end_string,
+            line_statement_prefix, line_comment_prefix, trim_blocks,
+            newline_sequence, frozenset(extensions), optimized, undefined,
+            finalize, autoescape, None, 0, False, None)
+        return env.from_string(source, template_class=cls)
+
+    @classmethod
+    def from_code(cls, environment, code, globals, uptodate=None):
+        """Creates a template object from compiled code and the globals.  This
+        is used by the loaders and environment to create a template object.
+        """
+        namespace = {
+            'environment':  environment,
+            '__file__':     code.co_filename
+        }
+        exec code in namespace
+        rv = cls._from_namespace(environment, namespace, globals)
+        rv._uptodate = uptodate
+        return rv
+
+    @classmethod
+    def from_module_dict(cls, environment, module_dict, globals):
+        """Creates a template object from a module.  This is used by the
+        module loader to create a template object.
+
+        .. versionadded:: 2.4
+        """
+        return cls._from_namespace(environment, module_dict, globals)
+
+    @classmethod
+    def _from_namespace(cls, environment, namespace, globals):
+        t = object.__new__(cls)
+        t.environment = environment
+        t.globals = globals
+        t.name = namespace['name']
+        t.filename = namespace['__file__']
+        t.blocks = namespace['blocks']
+
+        # render function and module
+        t.root_render_func = namespace['root']
+        t._module = None
+
+        # debug and loader helpers
+        t._debug_info = namespace['debug_info']
+        t._uptodate = None
+
+        # store the reference
+        namespace['environment'] = environment
+        namespace['__jinja_template__'] = t
+
+        return t
+
+    def render(self, *args, **kwargs):
+        """This method accepts the same arguments as the `dict` constructor:
+        A dict, a dict subclass or some keyword arguments.  If no arguments
+        are given the context will be empty.  These two calls do the same::
+
+            template.render(knights='that say nih')
+            template.render({'knights': 'that say nih'})
+
+        This will return the rendered template as unicode string.
+        """
+        vars = dict(*args, **kwargs)
+        try:
+            return concat(self.root_render_func(self.new_context(vars)))
+        except Exception:
+            exc_info = sys.exc_info()
+        return self.environment.handle_exception(exc_info, True)
+
+    def stream(self, *args, **kwargs):
+        """Works exactly like :meth:`generate` but returns a
+        :class:`TemplateStream`.
+        """
+        return TemplateStream(self.generate(*args, **kwargs))
+
+    def generate(self, *args, **kwargs):
+        """For very large templates it can be useful to not render the whole
+        template at once but evaluate each statement after another and yield
+        piece for piece.  This method basically does exactly that and returns
+        a generator that yields one item after another as unicode strings.
+
+        It accepts the same arguments as :meth:`render`.
+        """
+        vars = dict(*args, **kwargs)
+        try:
+            for event in self.root_render_func(self.new_context(vars)):
+                yield event
+        except Exception:
+            exc_info = sys.exc_info()
+        else:
+            return
+        yield self.environment.handle_exception(exc_info, True)
+
+    def new_context(self, vars=None, shared=False, locals=None):
+        """Create a new :class:`Context` for this template.  The vars
+        provided will be passed to the template.  Per default the globals
+        are added to the context.  If shared is set to `True` the data
+        is passed as it to the context without adding the globals.
+
+        `locals` can be a dict of local variables for internal usage.
+        """
+        return new_context(self.environment, self.name, self.blocks,
+                           vars, shared, self.globals, locals)
+
+    def make_module(self, vars=None, shared=False, locals=None):
+        """This method works like the :attr:`module` attribute when called
+        without arguments but it will evaluate the template on every call
+        rather than caching it.  It's also possible to provide
+        a dict which is then used as context.  The arguments are the same
+        as for the :meth:`new_context` method.
+        """
+        return TemplateModule(self, self.new_context(vars, shared, locals))
+
+    @property
+    def module(self):
+        """The template as module.  This is used for imports in the
+        template runtime but is also useful if one wants to access
+        exported template variables from the Python layer:
+
+        >>> t = Template('{% macro foo() %}42{% endmacro %}23')
+        >>> unicode(t.module)
+        u'23'
+        >>> t.module.foo()
+        u'42'
+        """
+        if self._module is not None:
+            return self._module
+        self._module = rv = self.make_module()
+        return rv
+
+    def get_corresponding_lineno(self, lineno):
+        """Return the source line number of a line number in the
+        generated bytecode as they are not in sync.
+        """
+        for template_line, code_line in reversed(self.debug_info):
+            if code_line <= lineno:
+                return template_line
+        return 1
+
+    @property
+    def is_up_to_date(self):
+        """If this variable is `False` there is a newer version available."""
+        if self._uptodate is None:
+            return True
+        return self._uptodate()
+
+    @property
+    def debug_info(self):
+        """The debug info mapping."""
+        return [tuple(map(int, x.split('='))) for x in
+                self._debug_info.split('&')]
+
+    def __repr__(self):
+        if self.name is None:
+            name = 'memory:%x' % id(self)
+        else:
+            name = repr(self.name)
+        return '<%s %s>' % (self.__class__.__name__, name)
+
+
+class TemplateModule(object):
+    """Represents an imported template.  All the exported names of the
+    template are available as attributes on this object.  Additionally
+    converting it into an unicode- or bytestrings renders the contents.
+    """
+
+    def __init__(self, template, context):
+        self._body_stream = list(template.root_render_func(context))
+        self.__dict__.update(context.get_exported())
+        self.__name__ = template.name
+
+    def __html__(self):
+        return Markup(concat(self._body_stream))
+
+    def __str__(self):
+        return unicode(self).encode('utf-8')
+
+    # unicode goes after __str__ because we configured 2to3 to rename
+    # __unicode__ to __str__.  because the 2to3 tree is not designed to
+    # remove nodes from it, we leave the above __str__ around and let
+    # it override at runtime.
+    def __unicode__(self):
+        return concat(self._body_stream)
+
+    def __repr__(self):
+        if self.__name__ is None:
+            name = 'memory:%x' % id(self)
+        else:
+            name = repr(self.__name__)
+        return '<%s %s>' % (self.__class__.__name__, name)
+
+
+class TemplateExpression(object):
+    """The :meth:`jinja2.Environment.compile_expression` method returns an
+    instance of this object.  It encapsulates the expression-like access
+    to the template with an expression it wraps.
+    """
+
+    def __init__(self, template, undefined_to_none):
+        self._template = template
+        self._undefined_to_none = undefined_to_none
+
+    def __call__(self, *args, **kwargs):
+        context = self._template.new_context(dict(*args, **kwargs))
+        consume(self._template.root_render_func(context))
+        rv = context.vars['result']
+        if self._undefined_to_none and isinstance(rv, Undefined):
+            rv = None
+        return rv
+
+
+class TemplateStream(object):
+    """A template stream works pretty much like an ordinary python generator
+    but it can buffer multiple items to reduce the number of total iterations.
+    Per default the output is unbuffered which means that for every unbuffered
+    instruction in the template one unicode string is yielded.
+
+    If buffering is enabled with a buffer size of 5, five items are combined
+    into a new unicode string.  This is mainly useful if you are streaming
+    big templates to a client via WSGI which flushes after each iteration.
+    """
+
+    def __init__(self, gen):
+        self._gen = gen
+        self.disable_buffering()
+
+    def dump(self, fp, encoding=None, errors='strict'):
+        """Dump the complete stream into a file or file-like object.
+        Per default unicode strings are written, if you want to encode
+        before writing specifiy an `encoding`.
+
+        Example usage::
+
+            Template('Hello {{ name }}!').stream(name='foo').dump('hello.html')
+        """
+        close = False
+        if isinstance(fp, basestring):
+            fp = file(fp, 'w')
+            close = True
+        try:
+            if encoding is not None:
+                iterable = (x.encode(encoding, errors) for x in self)
+            else:
+                iterable = self
+            if hasattr(fp, 'writelines'):
+                fp.writelines(iterable)
+            else:
+                for item in iterable:
+                    fp.write(item)
+        finally:
+            if close:
+                fp.close()
+
+    def disable_buffering(self):
+        """Disable the output buffering."""
+        self._next = self._gen.next
+        self.buffered = False
+
+    def enable_buffering(self, size=5):
+        """Enable buffering.  Buffer `size` items before yielding them."""
+        if size <= 1:
+            raise ValueError('buffer size too small')
+
+        def generator(next):
+            buf = []
+            c_size = 0
+            push = buf.append
+
+            while 1:
+                try:
+                    while c_size < size:
+                        c = next()
+                        push(c)
+                        if c:
+                            c_size += 1
+                except StopIteration:
+                    if not c_size:
+                        return
+                yield concat(buf)
+                del buf[:]
+                c_size = 0
+
+        self.buffered = True
+        self._next = generator(self._gen.next).next
+
+    def __iter__(self):
+        return self
+
+    def next(self):
+        return self._next()
+
+
+# hook in default template class.  if anyone reads this comment: ignore that
+# it's possible to use custom templates ;-)
+Environment.template_class = Template