text: import warnings
  from contextlib import contextmanager
  from copy import copy
  
  from django.utils.deprecation import RemovedInDjango20Warning
  
  # Hard-coded processor for easier use of CSRF protection.
  _builtin_context_processors = ('django.template.context_processors.csrf',)
  
  _current_app_undefined = object()
  
  
  class ContextPopException(Exception):
      "pop() has been called more times than push()"
      pass
  
  
  class ContextDict(dict):
      def __init__(self, context, *args, **kwargs):
          super(ContextDict, self).__init__(*args, **kwargs)
  
          context.dicts.append(self)
          self.context = context
  
      def __enter__(self):
          return self
  
      def __exit__(self, *args, **kwargs):
          self.context.pop()
  
  
  class BaseContext(object):
      def __init__(self, dict_=None):
          self._reset_dicts(dict_)
  
      def _reset_dicts(self, value=None):
          builtins = {'True': True, 'False': False, 'None': None}
          self.dicts = [builtins]
          if value is not None:
              self.dicts.append(value)
  
      def __copy__(self):
          duplicate = copy(super(BaseContext, self))
          duplicate.dicts = self.dicts[:]
          return duplicate
  
      def __repr__(self):
          return repr(self.dicts)
  
      def __iter__(self):
          for d in reversed(self.dicts):
              yield d
  
      def push(self, *args, **kwargs):
          return ContextDict(self, *args, **kwargs)
  
      def pop(self):
          if len(self.dicts) == 1:
              raise ContextPopException
          return self.dicts.pop()
  
      def __setitem__(self, key, value):
          "Set a variable in the current context"
          self.dicts[-1][key] = value
  
      def __getitem__(self, key):
          "Get a variable's value, starting at the current context and going upward"
          for d in reversed(self.dicts):
              if key in d:
                  return d[key]
          raise KeyError(key)
  
      def __delitem__(self, key):
          "Delete a variable from the current context"
          del self.dicts[-1][key]
  
      def has_key(self, key):
          for d in self.dicts:
              if key in d:
                  return True
          return False
  
      def __contains__(self, key):
          return self.has_key(key)
  
      def get(self, key, otherwise=None):
          for d in reversed(self.dicts):
              if key in d:
                  return d[key]
          return otherwise
  
      def setdefault(self, key, default=None):
          try:
              return self[key]
          except KeyError:
              self[key] = default
          return default
  
      def new(self, values=None):
          """
          Returns a new context with the same properties, but with only the
          values given in 'values' stored.
          """
          new_context = copy(self)
          new_context._reset_dicts(values)
          return new_context
  
      def flatten(self):
          """
          Returns self.dicts as one dictionary
          """
          flat = {}
          for d in self.dicts:
              flat.update(d)
          return flat
  
      def __eq__(self, other):
          """
          Compares two contexts by comparing theirs 'dicts' attributes.
          """
          if isinstance(other, BaseContext):
              # because dictionaries can be put in different order
              # we have to flatten them like in templates
              return self.flatten() == other.flatten()
  
          # if it's not comparable return false
          return False
  
  
  class Context(BaseContext):
      "A stack container for variable context"
      def __init__(self, dict_=None, autoescape=True,
              current_app=_current_app_undefined,
              use_l10n=None, use_tz=None):
          if current_app is not _current_app_undefined:
              warnings.warn(
                  "The current_app argument of Context is deprecated. Use "
                  "RequestContext and set the current_app attribute of its "
                  "request instead.", RemovedInDjango20Warning, stacklevel=2)
          self.autoescape = autoescape
          self._current_app = current_app
          self.use_l10n = use_l10n
          self.use_tz = use_tz
          self.render_context = RenderContext()
          # Set to the original template -- as opposed to extended or included
          # templates -- during rendering, see bind_template.
          self.template = None
          super(Context, self).__init__(dict_)
  
      @property
      def current_app(self):
          return None if self._current_app is _current_app_undefined else self._current_app
  
      @contextmanager
      def bind_template(self, template):
          if self.template is not None:
              raise RuntimeError("Context is already bound to a template")
          self.template = template
          try:
              yield
          finally:
              self.template = None
  
      def __copy__(self):
          duplicate = super(Context, self).__copy__()
          duplicate.render_context = copy(self.render_context)
          return duplicate
  
      def update(self, other_dict):
          "Pushes other_dict to the stack of dictionaries in the Context"
          if not hasattr(other_dict, '__getitem__'):
              raise TypeError('other_dict must be a mapping (dictionary-like) object.')
          self.dicts.append(other_dict)
          return other_dict
  
  
  class RenderContext(BaseContext):
      """
      A stack container for storing Template state.
  
      RenderContext simplifies the implementation of template Nodes by providing a
      safe place to store state between invocations of a node's `render` method.
  
      The RenderContext also provides scoping rules that are more sensible for
      'template local' variables. The render context stack is pushed before each
      template is rendered, creating a fresh scope with nothing in it. Name
      resolution fails if a variable is not found at the top of the RequestContext
      stack. Thus, variables are local to a specific template and don't affect the
      rendering of other templates as they would if they were stored in the normal
      template context.
      """
      def __iter__(self):
          for d in self.dicts[-1]:
              yield d
  
      def has_key(self, key):
          return key in self.dicts[-1]
  
      def get(self, key, otherwise=None):
          return self.dicts[-1].get(key, otherwise)
  
      def __getitem__(self, key):
          return self.dicts[-1][key]
  
  
  class RequestContext(Context):
      """
      This subclass of template.Context automatically populates itself using
      the processors defined in the engine's configuration.
      Additional processors can be specified as a list of callables
      using the "processors" keyword argument.
      """
      def __init__(self, request, dict_=None, processors=None,
              current_app=_current_app_undefined,
              use_l10n=None, use_tz=None):
          # current_app isn't passed here to avoid triggering the deprecation
          # warning in Context.__init__.
          super(RequestContext, self).__init__(
              dict_, use_l10n=use_l10n, use_tz=use_tz)
          if current_app is not _current_app_undefined:
              warnings.warn(
                  "The current_app argument of RequestContext is deprecated. "
                  "Set the current_app attribute of its request instead.",
                  RemovedInDjango20Warning, stacklevel=2)
          self._current_app = current_app
          self.request = request
          self._processors = () if processors is None else tuple(processors)
          self._processors_index = len(self.dicts)
          self.update({})         # placeholder for context processors output
  
      @contextmanager
      def bind_template(self, template):
          if self.template is not None:
              raise RuntimeError("Context is already bound to a template")
  
          self.template = template
          # Set context processors according to the template engine's settings.
          processors = (template.engine.template_context_processors +
                        self._processors)
          updates = {}
          for processor in processors:
              updates.update(processor(self.request))
          self.dicts[self._processors_index] = updates
  
          try:
              yield
          finally:
              self.template = None
              # Unset context processors.
              self.dicts[self._processors_index] = {}
  
      def new(self, values=None):
          new_context = super(RequestContext, self).new(values)
          # This is for backwards-compatibility: RequestContexts created via
          # Context.new don't include values from context processors.
          if hasattr(new_context, '_processors_index'):
              del new_context._processors_index
          return new_context
  
  
  def make_context(context, request=None):
      """
      Create a suitable Context from a plain dict and optionally an HttpRequest.
      """
      if request is None:
          context = Context(context)
      else:
          # The following pattern is required to ensure values from
          # context override those from template context processors.
          original_context = context
          context = RequestContext(request)
          if original_context:
              context.push(original_context)
      return context
  