module documentation

Support for results that aren't immediately available.

Maintainer: Glyph Lefkowitz

Class DebugInfo Deferred debug helper.
Class Deferred This is a callback which will be put off until later.
Class DeferredFilesystemLock A FilesystemLock that allows for a Deferred to be fired when the lock is acquired.
Class DeferredList DeferredList is a tool for collecting the results of several Deferreds.
Class DeferredLock A lock for event driven systems.
Class DeferredQueue An event driven queue.
Class DeferredSemaphore A semaphore for event driven systems.
Class waitForDeferred See deferredGenerator.
Exception AlreadyCalledError This error is raised when one of Deferred.callback or Deferred.errback is called after one of the two had already been called.
Exception AlreadyTryingToLockError Raised when DeferredFilesystemLock.deferUntilLocked is called twice on a single DeferredFilesystemLock.
Exception CancelledError This error is raised by default when a Deferred is cancelled.
Exception FailureGroup More than one failure occurred.
Exception FirstError First error to occur in a DeferredList if fireOnOneErrback is set.
Exception NotACoroutineError This error is raised when a coroutine is expected and something else is encountered.
Exception QueueOverflow Undocumented
Exception QueueUnderflow Undocumented
Exception TimeoutError This error is raised by default when a Deferred times out.
Function deferredGenerator 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.
Function ensureDeferred Schedule the execution of a coroutine that awaits/yields from Deferreds, wrapping it in a Deferred that will fire on success/failure of the coroutine. If a Deferred is passed to this function, it will be returned directly (mimicking the ...
Function execute Create a Deferred from a callable and arguments.
Function fail Return a Deferred that has already had .errback(result) called.
Function gatherResults Returns, via a Deferred, a list with the results of the given Deferreds - in effect, a "join" of multiple deferred operations.
Function getDebugging Determine whether Deferred debugging is enabled.
Function inlineCallbacks inlineCallbacks helps you write Deferred-using code that looks like a regular sequential function. For example:
Function logError Log and return failure.
Function maybeDeferred Invoke a function that may or may not return a Deferred or coroutine.
Function passthru Undocumented
Function race Select the first available result from the sequence of Deferreds and cancel the rest.
Function returnValue Return val from a inlineCallbacks generator.
Function setDebugging Enable or disable Deferred debugging.
Function succeed Return a Deferred that has already had .callback(result) called.
Function timeout Undocumented
Constant FAILURE Undocumented
Constant SUCCESS Undocumented
Type Alias DeferredCallback Undocumented
Type Alias DeferredErrback Undocumented
Variable log Undocumented
Class _CancellationStatus Cancellation status of an inlineCallbacks invocation.
Class _ConcurrencyPrimitive No class docstring; 0/1 instance variable, 2/7 methods documented
Class _Sentinel No summary
Exception _DefGen_Return Undocumented
Exception _InternalInlineCallbacksCancelledError A unique exception used only in _cancellableInlineCallbacks to verify that an inlineCallbacks is being cancelled as expected.
Function _addCancelCallbackToDeferred Helper for _cancellableInlineCallbacks to add _handleCancelInlineCallbacks as the first errback.
Function _cancellableInlineCallbacks Make an @inlineCallbacks cancellable.
Function _cancelledToTimedOutError A default translation function that translates Failures that are CancelledErrors to TimeoutErrors.
Function _deferGenerator See deferredGenerator.
Function _DeferredList Undocumented
Function _failthru Undocumented
Function _gotResultInlineCallbacks Helper for _inlineCallbacks to handle a nested Deferred firing.
Function _handleCancelInlineCallbacks Propagate the cancellation of an @inlineCallbacks to the Deferred it is waiting on.
Function _inlineCallbacks Carry out the work of inlineCallbacks.
Function _parseDeferredListResult Undocumented
Constant _NONE_KWARGS Undocumented
Constant _P Undocumented
Type Variable _NextResultT Undocumented
Type Variable _SelfResultT Undocumented
Type Variable _T Undocumented
Type Alias _CallbackChain Undocumented
Type Alias _CallbackKeywordArguments Undocumented
Type Alias _CallbackOrderedArguments Undocumented
Type Alias _DeferableGenerator Undocumented
Type Alias _DeferredListResultItemT Undocumented
Type Alias _DeferredListResultListT Undocumented
Type Alias _DeferredListSingleResultT Undocumented
Variable _oldPypyStack Undocumented
def deferredGenerator(f: Callable[..., _DeferableGenerator]) -> Callable[..., Deferred[object]]: (source)

Deprecated since version 15.0.0: 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.

Schedule the execution of a coroutine that awaits/yields from Deferreds, wrapping it in a Deferred that will fire on success/failure of the coroutine. If a Deferred is passed to this function, it will be returned directly (mimicking the asyncio.ensure_future function).

See Deferred.fromCoroutine for examples of coroutines.

Parameters
coro:Union[Coroutine[Deferred[Any], Any, _T], Generator[Deferred[Any], Any, _T], Deferred[_T]]The coroutine object to schedule, or a Deferred.
Returns
Deferred[_T]Undocumented
def execute(callable: Callable[_P, _T], *args: _P.args, **kwargs: _P.kwargs) -> Deferred[_T]: (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.

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

See succeed's docstring for rationale.

Parameters
result:Optional[Union[Failure, BaseException]]The same argument that Deferred.errback takes.
Returns
Deferred[Any]Undocumented
Raises
NoCurrentExceptionErrorIf result is None but there is no current exception state.
def gatherResults(deferredList: Iterable[Deferred[_T]], consumeErrors: bool = False) -> Deferred[List[_T]]: (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
deferredList:Iterable[Deferred[_T]]Undocumented
consumeErrors:bool(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.
Returns
Deferred[List[_T]]Undocumented
def getDebugging() -> bool: (source)

Determine whether Deferred debugging is enabled.

def inlineCallbacks(f: Callable[_P, Generator[Deferred[Any], Any, _T]]) -> Callable[_P, Deferred[_T]]: (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')

It is possible to use the return statement instead of returnValue:

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

You can cancel the Deferred returned from your inlineCallbacks generator before it is fired by your generator completing (either by reaching its end, a return statement, or by calling returnValue). A CancelledError will be raised from the yielded Deferred that has been cancelled if that Deferred does not otherwise suppress it.

def logError(err: Failure) -> Failure: (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.

@overload
def maybeDeferred(f: Callable[_P, Deferred[_T]], *args: _P.args, **kwargs: _P.kwargs) -> Deferred[_T]:
@overload
def maybeDeferred(f: Callable[_P, Coroutine[Deferred[Any], Any, _T]], *args: _P.args, **kwargs: _P.kwargs) -> Deferred[_T]:
@overload
def maybeDeferred(f: Callable[_P, _T], *args: _P.args, **kwargs: _P.kwargs) -> Deferred[_T]:
(source)

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

Call the given function with the given arguments. Then:

Parameters
f:Callable[_P, Union[Deferred[_T], Coroutine[Deferred[Any], Any, _T], _T]]The callable to invoke
*args:_P.argsThe arguments to pass to f
**kwargs:_P.kwargsThe keyword arguments to pass to f
Returns
Deferred[_T]The result of the function call, wrapped in a Deferred if necessary.
def passthru(arg: _T) -> _T: (source)

Undocumented

Select the first available result from the sequence of Deferreds and cancel the rest.

Returns
Deferred[tuple[int, _T]]A cancellable Deferred that fires with the index and output of the element of ds to have a success result first, or that fires with FailureGroup holding a list of their failures if they all fail.
def returnValue(val: object) -> NoReturn: (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 setDebugging(on: bool): (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 succeed(result: _T) -> Deferred[_T]: (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:_TThe result to give to the Deferred's 'callback' method.
Returns
Deferred[_T]Undocumented
def timeout(deferred: Deferred[object]): (source)

Deprecated since version 17.1.0: timeout was deprecated in Twisted 17.1.0; please use twisted.internet.defer.Deferred.addTimeout instead.

Undocumented

Undocumented

Value
False

Undocumented

Value
True
DeferredCallback = (source)

Undocumented

Value
Callable[..., object]
DeferredErrback = (source)

Undocumented

Value
Callable[..., object]

Undocumented

def _addCancelCallbackToDeferred(it: Deferred[_T], status: _CancellationStatus[_T]): (source)

Helper for _cancellableInlineCallbacks to add _handleCancelInlineCallbacks as the first errback.

Parameters
it:Deferred[_T]The Deferred to add the errback to.
status:_CancellationStatus[_T]a _CancellationStatus tracking the current status of gen
def _cancellableInlineCallbacks(gen: Union[Generator[Deferred[Any], object, _T], Coroutine[Deferred[Any], object, _T]]) -> Deferred[_T]: (source)

Make an @inlineCallbacks cancellable.

Parameters
gen:Union[Generator[Deferred[Any], object, _T], Coroutine[Deferred[Any], object, _T]]a generator object returned by calling a function or method decorated with @inlineCallbacks
Returns
Deferred[_T]Deferred for the @inlineCallbacks that is cancellable.
def _cancelledToTimedOutError(value: _T, timeout: float) -> _T: (source)

A default translation function that translates Failures that are CancelledErrors to TimeoutErrors.

Parameters
value:_TAnything
timeout:floatThe timeout
Returns
_TUndocumented
Raises
TimeoutErrorIf value is a Failure that is a CancelledError.
ExceptionIf value is a Failure that is not a CancelledError, it is re-raised.
Present Since
16.5
@overload
def _DeferredList(deferredList: Iterable[Deferred[_SelfResultT]], fireOnOneCallback: Literal[True], fireOnOneErrback: bool = False, consumeErrors: bool = False) -> Deferred[_DeferredListSingleResultT[_SelfResultT]]:
@overload
def _DeferredList(deferredList: Iterable[Deferred[_SelfResultT]], fireOnOneCallback: Literal[False] = False, fireOnOneErrback: bool = False, consumeErrors: bool = False) -> Deferred[_DeferredListResultListT[_SelfResultT]]:
(source)

Undocumented

def _failthru(arg: Failure) -> Failure: (source)

Undocumented

def _gotResultInlineCallbacks(r: object, waiting: List[Any], gen: Union[Generator[Deferred[Any], Any, _T], Coroutine[Deferred[Any], Any, _T]], status: _CancellationStatus[_T], context: _Context): (source)

Helper for _inlineCallbacks to handle a nested Deferred firing.

Parameters
r:objectThe result of the Deferred
waiting:List[Any]Whether the _inlineCallbacks was waiting, and the result.
gen:Union[Generator[Deferred[Any], Any, _T], Coroutine[Deferred[Any], Any, _T]]a generator object returned by calling a function or method decorated with @inlineCallbacks
status:_CancellationStatus[_T]a _CancellationStatus tracking the current status of gen
context:_Contextthe contextvars context to run `gen` in
def _handleCancelInlineCallbacks(result: Failure, status: _CancellationStatus[_T], /) -> Deferred[_T]: (source)

Propagate the cancellation of an @inlineCallbacks to the Deferred it is waiting on.

Parameters
result:FailureAn _InternalInlineCallbacksCancelledError from cancel().
status:_CancellationStatus[_T]a _CancellationStatus tracking the current status of gen
Returns
Deferred[_T]A new Deferred that the @inlineCallbacks generator can callback or errback through.
@_extraneous
def _inlineCallbacks(result: object, gen: Union[Generator[Deferred[Any], Any, _T], Coroutine[Deferred[Any], Any, _T]], status: _CancellationStatus[_T], context: _Context): (source)

Carry out the work of inlineCallbacks.

Iterate the generator produced by an @inlineCallbacks-decorated function, gen, send()ing it the results of each value yielded by that generator, until a Deferred is yielded, at which point a callback is added to that Deferred to call this function again.

Parameters
result:objectThe last result seen by this generator. Note that this is never a Deferred - by the time this function is invoked, the Deferred has been called back and this will be a particular result at a point in its callback chain.
gen:Union[Generator[Deferred[Any], Any, _T], Coroutine[Deferred[Any], Any, _T]]a generator object returned by calling a function or method decorated with @inlineCallbacks
status:_CancellationStatus[_T]a _CancellationStatus tracking the current status of gen
context:_Contextthe contextvars context to run `gen` in
def _parseDeferredListResult(resultList: List[_DeferredListResultItemT[_T]], fireOnOneErrback: bool = False, /) -> List[_T]: (source)

Undocumented

Undocumented

Value
ParamSpec('_P')
_NextResultT = (source)

Undocumented

Value
TypeVar('_NextResultT')
_SelfResultT = (source)

Undocumented

Value
TypeVar('_SelfResultT')

Undocumented

Value
TypeVar('_T')
_CallbackKeywordArguments = (source)

Undocumented

Value
Mapping[str, object]
_CallbackOrderedArguments = (source)

Undocumented

Value
Tuple[object, ...]
_DeferableGenerator = (source)

Undocumented

Value
Generator[object, None, None]
_DeferredListResultItemT = (source)

Undocumented

Value
Tuple[bool, _SelfResultT]
_DeferredListResultListT = (source)
_DeferredListSingleResultT = (source)

Undocumented

Value
Tuple[_SelfResultT, int]
_oldPypyStack = (source)

Undocumented