twisted.internet.defer : API documentation

Support for results that aren't immediately available.

Maintainer: Glyph Lefkowitz

Class	AlreadyCalledError	Undocumented
Class	CancelledError	This error is raised by default when a `Deferred` is cancelled.
Class	TimeoutError	This exception is deprecated. It is used only by the deprecated `Deferred.setTimeout` method.
Function	logError	Log and return failure.
Function	succeed	Return a `Deferred` that has already had `.callback(result)` called.
Function	fail	Return a `Deferred` that has already had `.errback(result)` called.
Function	execute	Create a `Deferred` from a callable and arguments.
Function	maybeDeferred	Invoke a function that may or may not return a `Deferred`.
Function	timeout	Undocumented
Function	passthru	Undocumented
Function	setDebugging	Enable or disable `Deferred` debugging.
Function	getDebugging	Determine whether `Deferred` debugging is enabled.
Class	Deferred	This is a callback which will be put off until later.
Class	DebugInfo	Deferred debug helper.
Class	FirstError	First error to occur in a `DeferredList` if `fireOnOneErrback` is set.
Class	DeferredList	`DeferredList` is a tool for collecting the results of several Deferreds.
Function	gatherResults	Returns, via a `Deferred`, a list with the results of the given `Deferred`s - in effect, a "join" of multiple deferred operations.
Class	waitForDeferred	See `deferredGenerator`.
Function	deferredGenerator	No summary
Function	returnValue	Return val from a `inlineCallbacks` generator.
Function	inlineCallbacks	inlineCallbacks helps you write `Deferred`-using code that looks like a regular sequential function. For example:
Class	DeferredLock	A lock for event driven systems.
Class	DeferredSemaphore	A semaphore for event driven systems.
Class	QueueOverflow	Undocumented
Class	QueueUnderflow	Undocumented
Class	DeferredQueue	An event driven queue.
Class	AlreadyTryingToLockError	Raised when `DeferredFilesystemLock.deferUntilLocked` is called twice on a single `DeferredFilesystemLock`.
Class	DeferredFilesystemLock	A `FilesystemLock` that allows for a `Deferred` to be fired when the lock is acquired.
Variable	_NO_RESULT	The result used to represent the fact that there is no result. Never ever ever use this as an actual result for a Deferred. You have been warned.
Variable	_CONTINUE	A marker left in `Deferred.callbacks` to indicate a Deferred chain. Always accompanied by a Deferred instance in the args tuple pointing at the Deferred which is chained to the Deferred which has this marker.
Function	_parseDListResult	Undocumented
Function	_deferGenerator	See `deferredGenerator`.
Class	_DefGen_Return	Undocumented
Function	_inlineCallbacks	See `inlineCallbacks`.
Class	_ConcurrencyPrimitive	No class docstring; 1/3 methods documented

_NO_RESULT =

The result used to represent the fact that there is no result. Never ever ever use this as an actual result for a Deferred. You have been warned.

_CONTINUE =

A marker left in Deferred.callbacks to indicate a Deferred chain. Always accompanied by a Deferred instance in the args tuple pointing at the Deferred which is chained to the Deferred which has this marker.

def logError(err): (source)

Log and return failure.

This method can be used as an errback that passes the failure on to the next errback unmodified. Note that if this is the last errback, and the deferred gets garbage collected after being this errback has been called, the clean up code logs it again.

def succeed(result): (source)

Return a Deferred that has already had .callback(result) called.

This is useful when you're writing synchronous code to an asynchronous interface: i.e., some code is calling you expecting a Deferred result, but you don't actually need to do anything asynchronous. Just return defer.succeed(theResult).

See fail for a version of this function that uses a failing Deferred rather than a successful one.

Parameters	result	The result to give to the Deferred's 'callback' method.
Returns	(type: `Deferred`)

def fail(result=None): (source)

Return a Deferred that has already had .errback(result) called.

See succeed's docstring for rationale.

Parameters	result	The same argument that `Deferred.errback` takes.
Returns	(type: `Deferred`)
Raises	NoCurrentExceptionError	If `result` is `None` but there is no current exception state.

def execute(callable, *args, **kw): (source)

Create a Deferred from a callable and arguments.

Call the given function with the given arguments. Return a Deferred which has been fired with its callback as the result of that invocation or its errback with a Failure for the exception thrown.

def maybeDeferred(f, *args, **kw): (source)

Invoke a function that may or may not return a Deferred.

Call the given function with the given arguments. If the returned object is a Deferred, return it. If the returned object is a Failure, wrap it with fail and return it. Otherwise, wrap it in succeed and return it. If an exception is raised, convert it to a Failure, wrap it in fail, and then return it.

Parameters	f	The callable to invoke (type: Any callable)
	args	The arguments to pass to `f`
	kw	The keyword arguments to pass to `f`
Returns	The result of the function call, wrapped in a `Deferred` if necessary. (type: `Deferred`)

def timeout(deferred): (source)

Undocumented

def passthru(arg): (source)

Undocumented

def setDebugging(on): (source)

Enable or disable Deferred debugging.

When debugging is on, the call stacks from creation and invocation are recorded, and added to any AlreadyCalledErrors we raise.

def getDebugging(): (source)

Determine whether Deferred debugging is enabled.

def _parseDListResult(l, fireOnOneErrback=False): (source)

Undocumented

def gatherResults(deferredList, consumeErrors=False): (source)

Returns, via a Deferred, a list with the results of the given Deferreds - in effect, a "join" of multiple deferred operations.

The returned Deferred will fire when all of the provided Deferreds have fired, or when any one of them has failed.

This method can be cancelled by calling the cancel method of the Deferred, all the Deferreds in the list will be cancelled.

This differs from DeferredList in that you don't need to parse the result for success/failure.

Parameters consumeErrors (keyword param) a flag, defaulting to False, indicating that failures in any of the given Deferreds should not be propagated to errbacks added to the individual Deferreds after this gatherResults invocation. Any such errors in the individual Deferreds will be converted to a callback result of None. This is useful to prevent spurious 'Unhandled error in Deferred' messages from being logged. This parameter is available since 11.1.0. (type: bool)

def _deferGenerator(g, deferred): (source)

See deferredGenerator.

def deferredGenerator(f): (source)

deferredGenerator was deprecated in Twisted 15.0.0; please use twisted.internet.defer.inlineCallbacks instead.

deferredGenerator and waitForDeferred help you write Deferred-using code that looks like a regular sequential function. Consider the use of inlineCallbacks instead, which can accomplish the same thing in a more concise manner.

There are two important functions involved: waitForDeferred, and deferredGenerator. They are used together, like this:

   @deferredGenerator
   def thingummy():
       thing = waitForDeferred(makeSomeRequestResultingInDeferred())
       yield thing
       thing = thing.getResult()
       print thing #the result! hoorj!

waitForDeferred returns something that you should immediately yield; when your generator is resumed, calling thing.getResult() will either give you the result of the Deferred if it was a success, or raise an exception if it was a failure. Calling getResult is absolutely mandatory. If you do not call it, your program will not work.

deferredGenerator takes one of these waitForDeferred-using generator functions and converts it into a function that returns a Deferred. The result of the Deferred will be the last value that your generator yielded unless the last value is a waitForDeferred instance, in which case the result will be None. If the function raises an unhandled exception, the Deferred will errback instead. Remember that return result won't work; use yield result; return in place of that.

Note that not yielding anything from your generator will make the Deferred result in None. Yielding a Deferred from your generator is also an error condition; always yield waitForDeferred(d) instead.

The Deferred returned from your deferred generator may also errback if your generator raised an exception. For example:

   @deferredGenerator
   def thingummy():
       thing = waitForDeferred(makeSomeRequestResultingInDeferred())
       yield thing
       thing = thing.getResult()
       if thing == 'I love Twisted':
           # will become the result of the Deferred
           yield 'TWISTED IS GREAT!'
           return
       else:
           # will trigger an errback
           raise Exception('DESTROY ALL LIFE')

Put succinctly, these functions connect deferred-using code with this 'fake blocking' style in both directions: waitForDeferred converts from a Deferred to the 'blocking' style, and deferredGenerator converts from the 'blocking' style to a Deferred.

def returnValue(val): (source)

Return val from a inlineCallbacks generator.

Note: this is currently implemented by raising an exception derived from BaseException. You might want to change any 'except:' clauses to an 'except Exception:' clause so as not to catch this exception.

Also: while this function currently will work when called from within arbitrary functions called from within the generator, do not rely upon this behavior.

def _inlineCallbacks(result, g, deferred): (source)

See inlineCallbacks.

def inlineCallbacks(f): (source)

inlineCallbacks helps you write Deferred-using code that looks like a regular sequential function. For example:

   @inlineCallbacks
   def thingummy():
       thing = yield makeSomeRequestResultingInDeferred()
       print(thing)  # the result! hoorj!

When you call anything that results in a Deferred, you can simply yield it; your generator will automatically be resumed when the Deferred's result is available. The generator will be sent the result of the Deferred with the 'send' method on generators, or if the result was a failure, 'throw'.

Things that are not Deferreds may also be yielded, and your generator will be resumed with the same object sent back. This means yield performs an operation roughly equivalent to maybeDeferred.

Your inlineCallbacks-enabled generator will return a Deferred object, which will result in the return value of the generator (or will fail with a failure object if your generator raises an unhandled exception). Note that you can't use return result to return a value; use returnValue(result) instead. Falling off the end of the generator, or simply using return will cause the Deferred to have a result of None.

Be aware that returnValue will not accept a Deferred as a parameter. If you believe the thing you'd like to return could be a Deferred, do this:

   result = yield result
   returnValue(result)

The Deferred returned from your deferred generator may errback if your generator raised an exception:

   @inlineCallbacks
   def thingummy():
       thing = yield makeSomeRequestResultingInDeferred()
       if thing == 'I love Twisted':
           # will become the result of the Deferred
           returnValue('TWISTED IS GREAT!')
       else:
           # will trigger an errback
           raise Exception('DESTROY ALL LIFE')

If you are using Python 3.3 or later, it is possible to use the return statement instead of returnValue:

   @inlineCallbacks
   def loadData(url):
       response = yield makeRequest(url)
       return json.loads(response)

API Documentation for Twisted, generated by pydoctor at 2016-04-04 15:02:49.

twisted.internet.defer module documentation

`twisted.internet.defer` module documentation