twisted.python.context.ContextTracker : API documentation

A ContextTracker provides a way to pass arbitrary key/value data up and down a call stack without passing them as parameters to the functions on that call stack.

This can be useful when functions on the top and bottom of the call stack need to cooperate but the functions in between them do not allow passing the necessary state. For example:

   from twisted.python.context import call, get

   def handleRequest(request):
       call({'request-id': request.id}, renderRequest, request.url)

   def renderRequest(url):
       renderHeader(url)
       renderBody(url)

   def renderHeader(url):
       return "the header"

   def renderBody(url):
       return "the body (request id=%r)" % (get("request-id"),)

This should be used sparingly, since the lack of a clear connection between the two halves can result in code which is difficult to understand and maintain.

Instance Variables contexts A list of dicts tracking the context state. Each new ContextTracker.callWithContext pushes a new dict onto this stack for the duration of the call, making the data available to the function called and restoring the previous data once it is complete..

Method	__init__	Undocumented
Method	callWithContext	Call `func(args, *kw)` such that the contents of `newContext` will be available for it to retrieve using `getContext`.
Method	getContext	Retrieve the value for a key from the context.

def callWithContext(self, newContext, func, *args, **kw): (source)

Call func(*args, **kw) such that the contents of newContext will be available for it to retrieve using getContext.

Parameters	newContext	A `dict` of data to push onto the context for the duration of the call to `func`.
	func	A callable which will be called.
	*args	Any additional positional arguments to pass to `func`.
	**kw	Any additional keyword arguments to pass to `func`.
Returns	Whatever is returned by `func`
Raises	Whatever is raised by `func`.

def getContext(self, key, default=None): (source)

Retrieve the value for a key from the context.

Parameters	key	The key to look up in the context.
	default	The value to return if `key` is not found in the context.
Returns	The value most recently remembered in the context for `key`.

t.p.c.ContextTracker : class documentation