django/template/context.py

   1 from django.conf import settings
   2 from django.core.exceptions import ImproperlyConfigured
   3
   4 _standard_context_processors = None
   5
   6 class ContextPopException(Exception):
   7     "pop() has been called more times than push()"
   8     pass
   9
  10 class Context(object):
  11     "A stack container for variable context"
  12     def __init__(self, dict_=None, autoescape=True):
  13         dict_ = dict_ or {}
  14         self.dicts = [dict_]
  15         self.autoescape = autoescape
  16
  17     def __repr__(self):
  18         return repr(self.dicts)
  19
  20     def __iter__(self):
  21         for d in self.dicts:
  22             yield d
  23
  24     def push(self):
  25         d = {}
  26         self.dicts = [d] + self.dicts
  27         return d
  28
  29     def pop(self):
  30         if len(self.dicts) == 1:
  31             raise ContextPopException
  32         return self.dicts.pop(0)
  33
  34     def __setitem__(self, key, value):
  35         "Set a variable in the current context"
  36         self.dicts[0][key] = value
  37
  38     def __getitem__(self, key):
  39         "Get a variable's value, starting at the current context and going upward"
  40         for d in self.dicts:
  41             if key in d:
  42                 return d[key]
  43         raise KeyError(key)
  44
  45     def __delitem__(self, key):
  46         "Delete a variable from the current context"
  47         del self.dicts[0][key]
  48
  49     def has_key(self, key):
  50         for d in self.dicts:
  51             if key in d:
  52                 return True
  53         return False
  54
  55     __contains__ = has_key
  56
  57     def get(self, key, otherwise=None):
  58         for d in self.dicts:
  59             if key in d:
  60                 return d[key]
  61         return otherwise
  62
  63     def update(self, other_dict):
  64         "Like dict.update(). Pushes an entire dictionary's keys and values onto the context."
  65         self.dicts = [other_dict] + self.dicts
  66         return other_dict
  67
  68 # This is a function rather than module-level procedural code because we only
  69 # want it to execute if somebody uses RequestContext.
  70 def get_standard_processors():
  71     global _standard_context_processors
  72     if _standard_context_processors is None:
  73         processors = []
  74         for path in settings.TEMPLATE_CONTEXT_PROCESSORS:
  75             i = path.rfind('.')
  76             module, attr = path[:i], path[i+1:]
  77             try:
  78                 mod = __import__(module, {}, {}, [attr])
  79             except ImportError, e:
  80                 raise ImproperlyConfigured('Error importing request processor module %s: "%s"' % (module, e))
  81             try:
  82                 func = getattr(mod, attr)
  83             except AttributeError:
  84                 raise ImproperlyConfigured('Module "%s" does not define a "%s" callable request processor' % (module, attr))
  85             processors.append(func)
  86         _standard_context_processors = tuple(processors)
  87     return _standard_context_processors
  88
  89 class RequestContext(Context):
  90     """
  91     This subclass of template.Context automatically populates itself using
  92     the processors defined in TEMPLATE_CONTEXT_PROCESSORS.
  93     Additional processors can be specified as a list of callables
  94     using the "processors" keyword argument.
  95     """
  96     def __init__(self, request, dict=None, processors=None):
  97         Context.__init__(self, dict)
  98         if processors is None:
  99             processors = ()
 100         else:
 101             processors = tuple(processors)
 102         for processor in get_standard_processors() + processors:
 103             self.update(processor(request))