context作为view与template之间的桥梁，理解它的工作原理对于djagno的模板工作机制至关重要。
class ContextDict(dict):#上下文词典，由词典可以通过context找到属于那个上下文，dicts是列表
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 ContextDict(dict)是用来保存数据的，它连接了context与dicts，该类可以作为with语句表达式。
class BaseContext(object):#上下文的基类
def __init__(self, dict_=None):
self._reset_dicts(dict_)
def _reset_dicts(self, value=None):#每个上下文都是以builtins作为第一个元素的
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):#调用push时会生成一个上下文词典
dicts = []
for d in args:
if isinstance(d, BaseContext):
dicts += d.dicts[1:]
else:
dicts.append(d)
return ContextDict(self, *dicts, **kwargs)
def pop(self):
if len(self.dicts) == 1:
raise ContextPopException
return self.dicts.pop()
def __setitem__(self, key, value):#执行context['var']=var时，是在dicts的最后一个元素添加。
"Set a variable in the current context"
self.dicts[-1][key] = value
def __getitem__(self, key):#从最后一个元素开始查找key对应的值
"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):
class RequestContext(Context):
class RenderContext(BaseContext):
Context 与RequestContext的区别：
def __init__(self, dict_=None, autoescape=True,
current_app=_current_app_undefined,
use_l10n=None, use_tz=None):
def __init__(self, request, dict_=None, processors=None,
current_app=_current_app_undefined,
use_l10n=None, use_tz=None):
由它们的初始化函数的参数来看RenderContext多了一个request，processors，少了autoescape。
Context的update函数分析：
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.')
if isinstance(other_dict, BaseContext):#如果other_dict是上下文实例，要把头与尾去掉，重新生成上下文词典
other_dict = other_dict.dicts[1:].pop()
return ContextDict(self, other_dict)
模板上下文处理器在什么地方调用？在调用结果如何影响context？
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.",
RemovedInDjango110Warning, 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)
# placeholder for context processors output
self.update({})
# empty dict for any new modifications
# (so that context processors don't overwrite them)
self.update({})
@contextmanager
def bind_template(self, template):#绑定模板时会调用全局的上下文处理器及该请求的。
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))#每个处理器返回一个词典，通过调用词典的更新函数进行合并
self.dicts[self._processors_index] = updates#self._processors_index为len(self.dicts)
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
C:\mez>python manage.py shell Python 2.7.10 (default, May 23 2015, 09:40:32) [MSC v.1500 32 bit (Intel)] In [1]: from django.template import context In [3]: dir(context) Out[3]: ['BaseContext', 'Context', 'ContextDict', 'ContextPopException', 'RemovedInDjango110Warning', 'RenderContext', 'RequestContext', '__builtins__', '__doc__', '__file__', '__name__', '__package__', '_builtin_context_processors', '_current_app_undefined', 'contextmanager', 'copy', 'make_context', 'warnings'] In [4]: c=context.Context() In [5]: c.__dict__ Out[5]: {'_current_app': <object at 0x1597d08>, 'autoescape': True, 'dicts': [{'False': False, 'None': None, 'True': True}], 'render_context': [{'False': False, 'None': None, 'True': True}], 'template': None, 'template_name': 'unknown', 'use_l10n': None, 'use_tz': None} In [6]: c.push() Out[6]: {} In [7]: c.__dict__ Out[7]: {'_current_app': <object at 0x1597d08>, 'autoescape': True, 'dicts': [{'False': False, 'None': None, 'True': True}, {}], 'render_context': [{'False': False, 'None': None, 'True': True}], 'template': None, 'template_name': 'unknown', 'use_l10n': None, 'use_tz': None} In [8]: c['page']='welcome' In [9]: c.__dict__ Out[9]: {'_current_app': <object at 0x1597d08>, 'autoescape': True, 'dicts': [{'False': False, 'None': None, 'True': True}, {'page': 'welcome'}], 'render_context': [{'False': False, 'None': None, 'True': True}], 'template': None, 'template_name': 'unknown', 'use_l10n': None, 'use_tz': None} In [10]: c['menu']='menus' In [11]: c.__dict__ Out[11]: {'_current_app': <object at 0x1597d08>, 'autoescape': True, 'dicts': [{'False': False, 'None': None, 'True': True}, {'menu': 'menus', 'page': 'welcome'}], 'render_context': [{'False': False, 'None': None, 'True': True}], 'template': None, 'template_name': 'unknown', 'use_l10n': None, 'use_tz': None} In [12]: c['page'] Out[12]: 'welcome' In [13]: d={1:2,3:4} In [14]: c['d']=d In [16]: c['d'] Out[16]: {1: 2, 3: 4} In [17]: c.push(d) Out[17]: {1: 2, 3: 4} In [18]: c.__dict__ Out[18]: {'_current_app': <object at 0x1597d08>, 'autoescape': True, 'dicts': [{'False': False, 'None': None, 'True': True}, {'d': {1: 2, 3: 4}, 'menu': 'menus', 'page': 'welcome'}, {1: 2, 3: 4}], 'render_context': [{'False': False, 'None': None, 'True': True}], 'template': None, 'template_name': 'unknown', 'use_l10n': None, 'use_tz': None} In [19]: c[1] Out[19]: 2
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