Unhandled error in deferred



Unhandled error in deferred

Post by SSamiK » Sun Jan 24, 2021 1:17 pm

So this happend on a fresh install of Linux Mint — I installed Deluge and deluged as per my normal routine.
Set everything up so that it worked.

But there is a couple issues — first of not all torrents shows in the thin client so I had to restart it a few times to get everything to show. Even on the host that runs borth deluge and deluged. Labels would not do «move when completed» as setup.

And all of a sudden deluged just won»t start anymore.
Throws out this bunch of lines:

lsb_release -a
No LSB modules are available.
Distributor ID: Linuxmint
Description: Linux Mint 20.1
Release: 20.1
Codename: ulyssa

deluged —version
deluged 2.0.3
libtorrent: 1.2.12.0
Python: 3.8.5
OS: Linux Linux Mint 20.1 ulyssa

Any ideas what I can do to fix this? Deluge always have been my favorite client so I really don’t want to move to something else.

Re: Unhandled error in Deferred:

Post by SSamiK » Mon Jan 25, 2021 1:19 pm

I have not been able to solve this yet, so please if anyone can chime in I would appreciate it much.
I tried purging Deluge and deluged from my system and reinstalling but no change. I admit not having spent a ton of time trying to figure this out, but that’s life.. Just cant find the same amount of time to spend on things like this as in younger years.

For the time being I’m checking out rTorrent and Qbit as possible replacements — both lack a thin client, so they might not fill the deluge-gap but they’ll have to do for now.

Re: Unhandled error in Deferred:

Post by shamael » Tue Jan 26, 2021 7:55 am

Re: Unhandled error in Deferred:

Post by ross104 » Tue Jan 26, 2021 6:42 pm

It helped me, might help you.

Re: Unhandled error in Deferred:

Post by mentor » Fri Feb 19, 2021 11:17 am

ross104 wrote:
Install patch log.py

It helped me, might help you.

How does one install a patch? I’m using the ppa:deluge-team/stable ppa.

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Unhandled error in Deferred #3397

Comments

d7laungani commented Aug 20, 2018

I looked at previous issues regarding this error and I could not find a similar problem. My own stems from a missing package that scrapy seems to need. It says ImportError: No module named ’emailext’ .

scrapy -version -v gives me

Scrapy : 1.5.0 lxml : 4.2.1.0 libxml2 : 2.9.8 cssselect : 1.0.3 parsel : 1.4.0 w3lib : 1.19.0 Twisted : 17.9.0 Python : 3.5.2 (v3.5.2:4def2a2901a5, Jun 26 2016, 10:47:25) — [GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] pyOpenSSL : 17.5.0 (OpenSSL 1.1.0g 2 Nov 2017) cryptography : 2.1.4 Platform : Darwin-16.7.0-x86_64-i386-64bit

The full stack trace is : `
Traceback (most recent call last):
File «/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/twisted/internet/defer.py», line 1386, in _inlineCallbacks
result = g.send(result)
File «/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/scrapy/crawler.py», line 80, in crawl
self.engine = self._create_engine()
File «/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/scrapy/crawler.py», line 105, in _create_engine
return ExecutionEngine(self, lambda _: self.stop())
File «/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/scrapy/core/engine.py», line 70, in init
self.scraper = Scraper(crawler)
File «/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/scrapy/core/scraper.py», line 71, in init
self.itemproc = itemproc_cls.from_crawler(crawler)
File «/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/scrapy/middleware.py», line 58, in from_crawler
return cls.from_settings(crawler.settings, crawler)
File «/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/scrapy/middleware.py», line 34, in from_settings
mwcls = load_object(clspath)
File «/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/scrapy/utils/misc.py», line 44, in load_object
mod = import_module(module)
File «/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/importlib/init.py», line 126, in import_module
return _bootstrap._gcd_import(name[level:], package, level)
File «», line 986, in _gcd_import
File «», line 969, in _find_and_load
File «», line 944, in _find_and_load_unlocked
File «», line 222, in _call_with_frames_removed
File «», line 986, in _gcd_import
File «», line 969, in _find_and_load
File «», line 956, in _find_and_load_unlocked
ImportError: No module named ’emailext’
2018-08-19 21:18:23 [scrapy.crawler] INFO: Overridden settings: <>
2018-08-19 21:18:23 [scrapy.middleware] INFO: Enabled extensions:
[‘scrapy.extensions.corestats.CoreStats’,
‘scrapy.extensions.logstats.LogStats’,
‘scrapy.extensions.telnet.TelnetConsole’,
‘scrapy.extensions.memusage.MemoryUsage’]
2018-08-19 21:18:23 [scrapy.middleware] INFO: Enabled downloader middlewares:
[‘scrapy.downloadermiddlewares.httpauth.HttpAuthMiddleware’,
‘scrapy.downloadermiddlewares.downloadtimeout.DownloadTimeoutMiddleware’,
‘scrapy.downloadermiddlewares.defaultheaders.DefaultHeadersMiddleware’,
‘scrapy.downloadermiddlewares.useragent.UserAgentMiddleware’,
‘scrapy.downloadermiddlewares.retry.RetryMiddleware’,
‘scrapy.downloadermiddlewares.redirect.MetaRefreshMiddleware’,
‘scrapy.downloadermiddlewares.httpcompression.HttpCompressionMiddleware’,
‘scrapy.downloadermiddlewares.redirect.RedirectMiddleware’,
‘scrapy.downloadermiddlewares.cookies.CookiesMiddleware’,
‘scrapy.downloadermiddlewares.httpproxy.HttpProxyMiddleware’,
‘scrapy.downloadermiddlewares.stats.DownloaderStats’]
2018-08-19 21:18:23 [scrapy.middleware] INFO: Enabled spider middlewares:
[‘scrapy.spidermiddlewares.httperror.HttpErrorMiddleware’,
‘scrapy.spidermiddlewares.offsite.OffsiteMiddleware’,
‘scrapy.spidermiddlewares.referer.RefererMiddleware’,
‘scrapy.spidermiddlewares.urllength.UrlLengthMiddleware’,
‘scrapy.spidermiddlewares.depth.DepthMiddleware’]
Unhandled error in Deferred:
2018-08-19 21:18:23 [twisted] CRITICAL: Unhandled error in Deferred:

2018-08-19 21:18:23 [twisted] CRITICAL:
Traceback (most recent call last):
File «/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/twisted/internet/defer.py», line 1386, in _inlineCallbacks
result = g.send(result)
File «/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/scrapy/crawler.py», line 80, in crawl
self.engine = self._create_engine()
File «/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/scrapy/crawler.py», line 105, in _create_engine
return ExecutionEngine(self, lambda _: self.stop())
File «/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/scrapy/core/engine.py», line 70, in init
self.scraper = Scraper(crawler)
File «/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/scrapy/core/scraper.py», line 71, in init
self.itemproc = itemproc_cls.from_crawler(crawler)
File «/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/scrapy/middleware.py», line 58, in from_crawler
return cls.from_settings(crawler.settings, crawler)
File «/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/scrapy/middleware.py», line 34, in from_settings
mwcls = load_object(clspath)
File «/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/scrapy/utils/misc.py», line 44, in load_object
mod = import_module(module)
File «/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/importlib/init.py», line 126, in import_module
return _bootstrap._gcd_import(name[level:], package, level)
File «», line 986, in _gcd_import
File «», line 969, in _find_and_load
File «», line 944, in _find_and_load_unlocked
File «», line 222, in _call_with_frames_removed
File «», line 986, in _gcd_import
File «», line 969, in _find_and_load
File «», line 956, in _find_and_load_unlocked
ImportError: No module named ’emailext’`

The text was updated successfully, but these errors were encountered:

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Deferred Reference

This document is a guide to the behaviour of the twisted.internet.defer.Deferred object, and to various ways you can use them when they are returned by functions.

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This document assumes that you are familiar with the basic principle that the Twisted framework is structured around: asynchronous, callback-based programming, where instead of having blocking code in your program or using threads to run blocking code, you have functions that return immediately and then begin a callback chain when data is available.

After reading this document, the reader should expect to be able to deal with most simple APIs in Twisted and Twisted-using code that return Deferreds.

  • what sorts of things you can do when you get a Deferred from a function call; and
  • how you can write your code to robustly handle errors in Deferred code.

Deferreds

Twisted uses the Deferred object to manage the callback sequence. The client application attaches a series of functions to the deferred to be called in order when the results of the asychronous request are available (this series of functions is known as a series of callbacks, or a callback chain), together with a series of functions to be called if there is an error in the asychronous request (known as a series of errbacks or an errback chain). The asychronous library code calls the first callback when the result is available, or the first errback when an error occurs, and the Deferred object then hands the results of each callback or errback function to the next function in the chain.

Callbacks

A twisted.internet.defer.Deferred is a promise that a function will at some point have a result. We can attach callback functions to a Deferred, and once it gets a result these callbacks will be called. In addition Deferreds allow the developer to register a callback for an error, with the default behavior of logging the error. The deferred mechanism standardizes the application programmer’s interface with all sorts of blocking or delayed operations.

Multiple callbacks

Multiple callbacks can be added to a Deferred. The first callback in the Deferred’s callback chain will be called with the result, the second with the result of the first callback, and so on. Why do we need this? Well, consider a Deferred returned by twisted.enterprise.adbapi — the result of a SQL query. A web widget might add a callback that converts this result into HTML, and pass the Deferred onwards, where the callback will be used by twisted to return the result to the HTTP client. The callback chain will be bypassed in case of errors or exceptions.

Visual Explanation

  1. Requesting method (data sink) requests data, gets Deferred object.
  2. Requesting method attaches callbacks to Deferred object.

  1. When the result is ready, give it to the Deferred object. .callback(result) if the operation succeeded, .errback(failure) if it failed. Note that failure is typically an instance of a twisted.python.failure.Failure instance.
  2. Deferred object triggers previously-added (call/err)back with the result or failure . Execution then follows the following rules, going down the chain of callbacks to be processed.
    • Result of the callback is always passed as the first argument to the next callback, creating a chain of processors.
    • If a callback raises an exception, switch to errback.
    • An unhandled failure gets passed down the line of errbacks, this creating an asynchronous analog to a series to a series of except: statements.
    • If an errback doesn’t raise an exception or return a twisted.python.failure.Failure instance, switch to callback.

Errbacks

Deferred’s error handling is modeled after Python’s exception handling. In the case that no errors occur, all the callbacks run, one after the other, as described above.

If the errback is called instead of the callback (e.g. because a DB query raised an error), then a twisted.python.failure.Failure is passed into the first errback (you can add multiple errbacks, just like with callbacks). You can think of your errbacks as being like except blocks of ordinary Python code.

Unless you explicitly raise an error in an except block, the Exception is caught and stops propagating, and normal execution continues. The same thing happens with errbacks: unless you explicitly return a Failure or (re-)raise an exception, the error stops propagating, and normal callbacks continue executing from that point (using the value returned from the errback). If the errback does return a Failure or raise an exception, then that is passed to the next errback, and so on.

Note: If an errback doesn’t return anything, then it effectively returns None , meaning that callbacks will continue to be executed after this errback. This may not be what you expect to happen, so be careful. Make sure your errbacks return a Failure (probably the one that was passed to it), or a meaningful return value for the next callback.

Also, twisted.python.failure.Failure instances have a useful method called trap, allowing you to effectively do the equivalent of:

If none of arguments passed to failure.trap match the error encapsulated in that Failure , then it re-raises the error.

There’s another potential gotcha here. There’s a method twisted.internet.defer.Deferred.addCallbacks which is similar to, but not exactly the same as, addCallback followed by addErrback . In particular, consider these two cases:

If an error occurs in callback1 , then for Case 1 errback1 will be called with the failure. For Case 2, errback2 will be called. Be careful with your callbacks and errbacks.

What this means in a practical sense is in Case 1, the callback in line A will handle a success condition from getDeferredFromSomewhere , and the errback in line B will handle any errors that occur from either the upstream source, or that occur in A. In Case 2, the errback in line C will only handle an error condition raised by getDeferredFromSomewhere , it will not do any handling of errors raised in callback1 .

Unhandled Errors

If a Deferred is garbage-collected with an unhandled error (i.e. it would call the next errback if there was one), then Twisted will write the error’s traceback to the log file. This means that you can typically get away with not adding errbacks and still get errors logged. Be careful though; if you keep a reference to the Deferred around, preventing it from being garbage-collected, then you may never see the error (and your callbacks will mysteriously seem to have never been called). If unsure, you should explicitly add an errback after your callbacks, even if all you do is:

Handling either synchronous or asynchronous results

In some applications, there are functions that might be either asynchronous or synchronous. For example, a user authentication function might be able to check in memory whether a user is authenticated, allowing the authentication function to return an immediate result, or it may need to wait on network data, in which case it should return a Deferred to be fired when that data arrives. However, a function that wants to check if a user is authenticated will then need to accept both immediate results and Deferreds.

In this example, the library function authenticateUser uses the application function isValidUser to authenticate a user:

However, it assumes that isValidUser returns immediately, whereas isValidUser may actually authenticate the user asynchronously and return a Deferred. It is possible to adapt this trivial user authentication code to accept either a synchronous isValidUser or an asynchronous isValidUser , allowing the library to handle either type of function. It is, however, also possible to adapt synchronous functions to return Deferreds. This section describes both alternatives: handling functions that might be synchronous or asynchronous in the library function ( authenticateUser ) or in the application code.

Handling possible Deferreds in the library code

Here is an example of a synchronous user authentication function that might be passed to authenticateUser :

However, here’s an asynchronousIsValidUser function that returns a Deferred:

Our original implementation of authenticateUser expected isValidUser to be synchronous, but now we need to change it to handle both synchronous and asynchronous implementations of isValidUser . For this, we use maybeDeferred to call isValidUser , ensuring that the result of isValidUser is a Deferred, even if isValidUser is a synchronous function:

Now isValidUser could be either synchronousIsValidUser or asynchronousIsValidUser .

It is also possible to modify synchronousIsValidUser to return a Deferred, see Generating Deferreds for more information.

DeferredList

Sometimes you want to be notified after several different events have all happened, rather than waiting for each one individually. For example, you may want to wait for all the connections in a list to close. twisted.internet.defer.DeferredList is the way to do this.

To create a DeferredList from multiple Deferreds, you simply pass a list of the Deferreds you want it to wait for:

You can now treat the DeferredList like an ordinary Deferred; you can call addCallbacks and so on. The DeferredList will call its callback when all the deferreds have completed. The callback will be called with a list of the results of the Deferreds it contains, like so:

A standard DeferredList will never call errback, but failures in Deferreds passed to a DeferredList will still errback unless consumeErrors is passed True . See below for more details about this and other flags which modify the behavior of DeferredList.

If you want to apply callbacks to the individual Deferreds that go into the DeferredList, you should be careful about when those callbacks are added. The act of adding a Deferred to a DeferredList inserts a callback into that Deferred (when that callback is run, it checks to see if the DeferredList has been completed yet). The important thing to remember is that it is this callback which records the value that goes into the result list handed to the DeferredList’s callback.

Therefore, if you add a callback to the Deferred after adding the Deferred to the DeferredList, the value returned by that callback will not be given to the DeferredList’s callback. To avoid confusion, we recommend not adding callbacks to a Deferred once it has been used in a DeferredList.

Other behaviours

DeferredList accepts three keyword arguments that modify its behaviour: fireOnOneCallback , fireOnOneErrback and consumeErrors . If fireOnOneCallback is set, the DeferredList will immediately call its callback as soon as any of its Deferreds call their callback. Similarly, fireOnOneErrback will call errback as soon as any of the Deferreds call their errback. Note that DeferredList is still one-shot, like ordinary Deferreds, so after a callback or errback has been called the DeferredList will do nothing further (it will just silently ignore any other results from its Deferreds).

The fireOnOneErrback option is particularly useful when you want to wait for all the results if everything succeeds, but also want to know immediately if something fails.

The consumeErrors argument will stop the DeferredList from propagating any errors along the callback chains of any Deferreds it contains (usually creating a DeferredList has no effect on the results passed along the callbacks and errbacks of their Deferreds). Stopping errors at the DeferredList with this option will prevent Unhandled error in Deferred warnings from the Deferreds it contains without needing to add extra errbacks 1 . Passing a true value for the consumeErrors parameter will not change the behavior of fireOnOneCallback or fireOnOneErrback .

gatherResults

A common use for DeferredList is to «join» a number of parallel asynchronous operations, finishing successfully if all of the operations were successful, or failing if any one of the operations fails. In this case, twisted.internet.defer.gatherResults is a useful shortcut:

The consumeErrors argument has the same meaning as it does for DeferredList : if true, it causes gatherResults to consume any errors in the passed-in Deferreds. Always use this argument unless you are adding further callbacks or errbacks to the passed-in Deferreds, or unless you know that they will not fail. Otherwise, a failure will result in an unhandled error being logged by Twisted. This argument is available since Twisted 11.1.0.

Class Overview

This is an overview API reference for Deferred from the point of using a Deferred returned by a function. It is not meant to be a substitute for the docstrings in the Deferred class, but can provide guidelines for its use.

There is a parallel overview of functions used by the Deferred’s creator in Generating Deferreds.

Basic Callback Functions
  • addCallbacks(self, callback[, errback, callbackArgs, callbackKeywords, errbackArgs, errbackKeywords])

This is the method you will use to interact with Deferred. It adds a pair of callbacks parallel to each other (see diagram above) in the list of callbacks made when the Deferred is called back to. The signature of a method added using addCallbacks should be myMethod(result, *methodArgs, **methodKeywords) . If your method is passed in the callback slot, for example, all arguments in the tuple callbackArgs will be passed as *methodArgs to your method.

There are various convenience methods that are derivative of addCallbacks. I will not cover them in detail here, but it is important to know about them in order to create concise code.

    addCallback(callback, *callbackArgs, **callbackKeywords)

Adds your callback at the next point in the processing chain, while adding an errback that will re-raise its first argument, not affecting further processing in the error case.

Note that, while addCallbacks (plural) requires the arguments to be passed in a tuple, addCallback (singular) takes all its remaining arguments as things to be passed to the callback function. The reason is obvious: addCallbacks (plural) cannot tell whether the arguments are meant for the callback or the errback, so they must be specifically marked by putting them into a tuple. addCallback (singular) knows that everything is destined to go to the callback, so it can use Python’s * and ** syntax to collect the remaining arguments.

addErrback(errback, *errbackArgs, **errbackKeywords)

Adds your errback at the next point in the processing chain, while adding a callback that will return its first argument, not affecting further processing in the success case.

addBoth(callbackOrErrback, *callbackOrErrbackArgs, **callbackOrErrbackKeywords)

This method adds the same callback into both sides of the processing chain at both points. Keep in mind that the type of the first argument is indeterminate if you use this method! Use it for finally: style blocks.

Chaining Deferreds

If you need one Deferred to wait on another, all you need to do is return a Deferred from a method added to addCallbacks. Specifically, if you return Deferred B from a method added to Deferred A using A.addCallbacks, Deferred A’s processing chain will stop until Deferred B’s .callback() method is called; at that point, the next callback in A will be passed the result of the last callback in Deferred B’s processing chain at the time.

If this seems confusing, don’t worry about it right now — when you run into a situation where you need this behavior, you will probably recognize it immediately and realize why this happens. If you want to chain deferreds manually, there is also a convenience method to help you.

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