twisted.internet.defer.Deferred : API documentation

This is a callback which will be put off until later.

Why do we want this? Well, in cases where a function in a threaded program would block until it gets a result, for Twisted it should not block. Instead, it should return a Deferred.

This can be implemented for protocols that run over the network by writing an asynchronous protocol for twisted.internet. For methods that come from outside packages that are not under our control, we use threads (see for example twisted.enterprise.adbapi).

For more information about Deferreds, see doc/howto/defer.html or http://twistedmatrix.com/projects/core/documentation/howto/defer.html

When creating a Deferred, you may provide a canceller function, which will be called by d.cancel() to let you do any clean-up necessary if the user decides not to wait for the deferred to complete.

Method	__init__	Initialize a `Deferred`.
Method	addCallbacks	Add a pair of callbacks (success and error) to this `Deferred`.
Method	addCallback	Convenience method for adding just a callback.
Method	addErrback	Convenience method for adding just an errback.
Method	addBoth	Convenience method for adding a single callable as both a callback and an errback.
Method	chainDeferred	Chain another `Deferred` to this `Deferred`.
Method	callback	Run all success callbacks that have been added to this `Deferred`.
Method	errback	Run all error callbacks that have been added to this `Deferred`.
Method	pause	Stop processing on a `Deferred` until `unpause`() is called.
Method	unpause	Process all callbacks made since `pause`() was called.
Method	cancel	Cancel this `Deferred`.
Method	setTimeout	Set a timeout function to be triggered if I am not called.
Method	__str__	Undocumented
Method	_continue	Undocumented
Method	_startRunCallbacks	Undocumented
Method	_runCallbacks	Undocumented

def __init__(self, canceller=None): (source)

overridden in twisted.internet.defer.DeferredList, twisted.persisted.crefutil._Defer

Initialize a Deferred.

Parameters

canceller

a callable used to stop the pending operation scheduled by this Deferred when Deferred.cancel is invoked. The canceller will be passed the deferred whose cancelation is requested (i.e., self).

If a canceller is not given, or does not invoke its argument's callback or errback method, Deferred.cancel will invoke Deferred.errback with a CancelledError.

Note that if a canceller is not given, callback or errback may still be invoked exactly once, even though defer.py will have already invoked errback, as described above. This allows clients of code which returns a Deferred to cancel it without requiring the Deferred instantiator to provide any specific implementation support for cancellation. New in 10.0. (type: a 1-argument callable which takes a Deferred. The return result is ignored. )

def addCallbacks(self, callback, errback=None, callbackArgs=None, callbackKeywords=None, errbackArgs=None, errbackKeywords=None): (source)

Add a pair of callbacks (success and error) to this Deferred.

These will be executed when the 'master' callback is run.

def addCallback(self, callback, *args, **kw): (source)

Convenience method for adding just a callback.

See addCallbacks.

def addErrback(self, errback, *args, **kw): (source)

Convenience method for adding just an errback.

See addCallbacks.

def addBoth(self, callback, *args, **kw): (source)

Convenience method for adding a single callable as both a callback and an errback.

See addCallbacks.

def chainDeferred(self, d): (source)

Chain another Deferred to this Deferred.

This method adds callbacks to this Deferred to call d's callback or errback, as appropriate. It is merely a shorthand way of performing the following:

   self.addCallbacks(d.callback, d.errback)

When you chain a deferred d2 to another deferred d1 with d1.chainDeferred(d2), you are making d2 participate in the callback chain of d1. Thus any event that fires d1 will also fire d2. However, the converse is not true; if d2 is fired d1 will not be affected.

def callback(self, result): (source)

Run all success callbacks that have been added to this Deferred.

Each callback will have its result passed as the first argument to the next; this way, the callbacks act as a 'processing chain'. If the success-callback returns a Failure or raises an Exception, processing will continue on the *error* callback chain. If a callback (or errback) returns another Deferred, this Deferred will be chained to it (and further callbacks will not run until that Deferred has a result).

def errback(self, fail=None): (source)

Run all error callbacks that have been added to this Deferred.

Each callback will have its result passed as the first argument to the next; this way, the callbacks act as a 'processing chain'. Also, if the error-callback returns a non-Failure or doesn't raise an Exception, processing will continue on the *success*-callback chain.

If the argument that's passed to me is not a failure.Failure instance, it will be embedded in one. If no argument is passed, a failure.Failure instance will be created based on the current traceback stack.

Passing a string as `fail' is deprecated, and will be punished with a warning message.

Raises NoCurrentExceptionError If fail is None but there is no current exception state.

def pause(self): (source)

Stop processing on a Deferred until unpause() is called.

def unpause(self): (source)

Process all callbacks made since pause() was called.

def cancel(self): (source)

Cancel this Deferred.

If the Deferred has not yet had its errback or callback method invoked, call the canceller function provided to the constructor. If that function does not invoke callback or errback, or if no canceller function was provided, errback with CancelledError.

If this Deferred is waiting on another Deferred, forward the cancellation to the other Deferred.

def _continue(self, result): (source)

Undocumented

def _startRunCallbacks(self, result): (source)

Undocumented

def _runCallbacks(self): (source)

Undocumented

def setTimeout(self, seconds, *args, timeoutFunc=timeout, **kw): (source)

Set a timeout function to be triggered if I am not called.

Parameters	seconds	How long to wait (from now) before firing the `timeoutFunc`.
	timeoutFunc	will receive the `Deferred` and args, *kw as its arguments. The default `timeoutFunc` will call the errback with a `TimeoutError`.

t.i.d.Deferred : class documentation