Mailman 3 নভেম্বর 2024 - Python-list

How to break while loop based on events raised in a thread (Python 2.7)
by marc nicole 27 নভেম্বর, 2024

27 নভেম্বর, 2024

I am using the below class1 code to detect some event through the method check_for_the_event() # Some class1def check_for_the_event(self): thread1 = threading.Timer(2, self.check_for_the_event) thread1.start()# some processingif event is detected: self.event_ok = Trueelse: self.event_ok = False then I pass an instance of that class to the below class to know when the event is on or off and act upon its value accordingly using the following below code: # execution of other part of the program (where self.another_class_instance.event_ok = False and self.some_other_condition is true) current_time = current_time_some_cond = current_max_time = time.time() while not self.another_class_instance.event_ok and self.some_other_condition: while self.some_other_condition and not self.another_class_instance.event_ok:#self.some_other_condition takes up to 10 secs to be checked (minimum 5 secs) if time.time() > current_time + 5: current_time = time.time() # some processing else: while not self.another_class_instance.event_ok: #processing if time.time() > current_max_time + 60 * 2 and not self.another_class_instance.event_ok: #some other processing if time.time() > current_time_some_cond + 10 and not self.cond1 and not self.another_class_instance.event_ok: # some processing that takes 2-3 seconds self.cond1 = True current_time_some_cond = time.time() elif self.cond1 and time.time() > current_time_some_cond + 10 and not self.another_class_instance.event_ok: current_time_some_cond = time.time() #some other processing that takes 2-3 seconds else: pass else: pass The problem is the real time execution of the program (in class2) requires an instant check to be performed and that cannot wait until the current loop instructions finish, and I want is to break out of the outer while loop if the event is on without further checking any other condition. for now I perform multiple checks at each if or while statement, but is there a IO async based method that breaks out of the loop when the event is raised in the thread?

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[RELEASE] Python 3.14.0 alpha 2 is out
by Hugo van Kemenade 19 নভেম্বর, 2024

19 নভেম্বর, 2024

Alpha 2? But Alpha 1 only just came out! https://www.python.org/downloads/release/python-3140a2/ This is an early developer preview of Python 3.14 Major new features of the 3.14 series, compared to 3.13: Python 3.14 is still in development. This release, 3.14.0a2 is the second of seven planned alpha releases. Alpha releases are intended to make it easier to test the current state of new features and bug fixes and to test the release process. During the alpha phase, features may be added up until the start of the beta phase (2025-05-06) and, if necessary, may be modified or deleted up until the release candidate phase (2025-07-22). Please keep in mind that this is a preview release and its use is not recommended for production environments. Many new features for Python 3.14 are still being planned and written. Among the new major new features and changes so far: * PEP 649: deferred evaluation of annotations * PEP 741: Python configuration C API * PEP 761: Python 3.14 and onwards no longer provides PGP signatures for release artifacts. Instead, Sigstore is recommended for verifiers. * Improved error messages * (Hey, fellow core developer, if a feature you find important is missing from this list, let Hugo know.) The next pre-release of Python 3.14 will be 3.14.0a3, currently scheduled for 2024-12-17. More resources * Online documentation: https://docs.python.org/3.14/ * PEP 745, 3.14 Release Schedule: https://peps.python.org/pep-0719/ * Report bugs at https://github.com/python/cpython/issues * Help fund Python and its community: https://www.python.org/psf/donations/ And now for something completely different Ludolph van Ceulen (1540-1610) was a fencing and mathematics teacher in Leiden, Netherlands, and spent around 25 years calculating π (or pi), using essentially the same methods Archimedes employed some seventeen hundred years earlier. Archimedes estimated π by calculating the circumferences of polygons that fit just inside and outside of a circle, reasoning the circumference of the circle lies between these two values. Archimedes went up to polygons with 96 sides, for a value between 3.1408 and 3.1428, which is accurate to two decimal places. Van Ceulen used a polygon with half a billion sides. He published a 20-decimal value in his 1596 book Vanden Circkel (“On the Circle”), and later expanded it to 35 decimals: 3.14159265358979323846264338327950288 Van Ceulen’s 20 digits is more than enough precision for any conceivable practical purpose. For example, even if a printed circle was perfect down to the atomic scale, the thermal vibrations of the molecules of ink would make most of those digits physically meaningless. NASA Jet Propulsion Laboratory’s highest accuracy calculations, for interplanetary navigation, uses 15 decimals: 3.141592653589793. At Van Ceulen’s request, his upper and lower bounds for π were engraved on his tombstone in Leiden. The tombstone was eventually lost but restored in 2000. In the Netherlands and Germany, π is sometimes referred to as the “Ludolphine number”, after Van Ceulen. Enjoy the new release Thanks to all of the many volunteers who help make Python Development and these releases possible! Please consider supporting our efforts by volunteering yourself or through organisation contributions to the Python Software Foundation. Regards from a chilly Helsinki with snow on the way, Your release team, Hugo van Kemenade Ned Deily Steve Dower Łukasz Langa

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Re: FileNotFoundError thrown due to file name in file, rather than file itself
by Jon Ribbens 14 নভেম্বর, 2024

14 নভেম্বর, 2024

On 2024-11-14, Michael Torrie <torriem(a)gmail.com> wrote: > On 11/14/24 12:03 AM, Left Right wrote: >>> On any Unix system this is untrue. Rotating a log file is quite simple: >> >> I realized I posted this without cc'ing the list: >> http://jdebp.info/FGA/do-not-use-logrotate.html . >> >> The link above gives a more detailed description of why log rotation >> on the Unix system is not only not simple, but is, in fact, >> unreliable. > > Nothing in that article contradicts what I said about renaming log > files. His argument is that renaming log files messes with tail -F, and > therefore broken and unreliable. Which a pretty strange argument. tail > -F might not see some data during the rotation, but the log files > themselves don't miss anything, which was my contention. In all my > years of sysadmin-ing I have never once worried about problems GNU tail > might have with a file that gets rotated out from under you. Not sure > why the author is so fixated on it. I really wouldn't worry about anything Jonathan de Boyne Pollard says.

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Re: FileNotFoundError thrown due to file name in file, rather than file itself
by Loris Bennett 14 নভেম্বর, 2024

14 নভেম্বর, 2024

Left Right <olegsivokon(a)gmail.com> writes: > Poor error reporting is a very common problem in programming. Python > is not anything special in this case. Of course, it would've been > better if the error reported what file wasn't found. But, usually > these problems are stacking, like in your code. Unfortunately, it's > your duty, as the language user, to anticipate those problems and act > accordingly. Now you've learned that the one file you believe that > could be the source for the error isn't the only one--well, adjust > your code to differentiate between those two (and potentially other?) > cases. There's very little else you can do beside that. > > NB. On the system level, the error has no information about what file > wasn't found. It simply returns some numeric value (the famous > ENOENT) in case when the system call to open a file fails. Python > could've been more helpful by figuring out what path caused the > problem and printing that in the error message, but it doesn't... > That's why I, myself, never use the vanilla FileNotFoundError, I > always re-rise it with a customized version that incorporates the > information about the missing file in the error message. That sounds like a good idea. > NB2. It's always a bad idea to print logs to files. Any sysadmin / > ops / infra person worth their salt will tell you that. The only > place the logs should go to is the standard error. There are true and > tried tools that can pick up logs from that point on, and do with them > whatever your heart desires. That is, of course, unless you are > creating system tools for universal log management (in which case, I'd > question the choice of Python as a suitable language for such a task). > Unfortunately, even though this has been common knowledge for decades, > it's still elusive in the world of application development :| I am not entirely convinced by NB2. I am, in fact, a sort of sysadmin person and most of my programs write to a log file. The programs are also moderately complex, so a single program might access a database, query an LDAP server, send email etc., so potentially quite a lot can go wrong. They are also not programs whose output I would pipe to another command. What would be the advantage of logging to stderr? Quite apart from that, I find having a log file a useful for debugging when I am developing. Cheers, Loris > On Mon, Nov 11, 2024 at 4:00 PM Loris Bennett via Python-list > <python-list(a)python.org> wrote: >> >> Hi, >> >> I have the following in my program: >> >> try: >> logging.config.fileConfig(args.config_file) >> config = configparser.ConfigParser() >> config.read(args.config_file) >> if args.verbose: >> print(f"Configuration file: {args.config_file}") >> except FileNotFoundError: >> print(f"Error: configuration file {args.config_file} not found. Exiting.") >> sys.exit(0) >> >> and when I ran the program I got the error >> >> Error: configuration file /usr/local/etc/sc_mailer not found. Exiting. >> >> However, this file *does* exist and *can* be read. By checking the >> 'filename' attribute of the exception I discovered that the problem was >> the log file defined *in* the config file, namely >> >> [handler_fileHandler] >> class=FileHandler >> level=DEBUG >> formatter=defaultFormatter >> args=('/var/log/my_prog.log', 'a') >> >> This log file did not exist. The exception is thrown by >> >> logging.config.fileConfig(args.config_file) >> >> My questions are: >> >> 1. Should I be surprised by this behaviour? >> 2. In terms of generating a helpful error message, how should one >> distinguish between the config file not existing and the log file not >> existing? >> >> Cheers, >> >> Loris >> >> -- >> This signature is currently under constuction. >> -- >> https://mail.python.org/mailman/listinfo/python-list -- Dr. Loris Bennett (Herr/Mr) FUB-IT, Freie Universität Berlin

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Re: FileNotFoundError thrown due to file name in file, rather than file itself
by Loris Bennett 13 নভেম্বর, 2024

13 নভেম্বর, 2024

Chris Angelico <rosuav(a)gmail.com> writes: > On Tue, 12 Nov 2024 at 01:59, Loris Bennett via Python-list > <python-list(a)python.org> wrote: >> 2. In terms of generating a helpful error message, how should one >> distinguish between the config file not existing and the log file not >> existing? > > By looking at the exception's attributes rather than assuming and > hard-coding the path in your message? Or, even better, just let the > exception bubble. As Dieter also pointed out, I obviously made a mistake in assuming that I knew what 'FileNotFound' was referring to. However, it strikes me as not immediately obvious that the logging file must exist at this point. I can imagine a situation in which I want to configure a default log file and create it if it missing. Cheers, Loris -- This signature is currently under constuction.

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ANN: eGenix PyRun - One file Python Runtime 2.6.0
by eGenix Team 13 নভেম্বর, 2024

13 নভেম্বর, 2024

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Re: FileNotFoundError thrown due to file name in file, rather than file itself
by Greg Ewing 13 নভেম্বর, 2024

13 নভেম্বর, 2024

On 13/11/24 8:10 am, Left Right wrote: > since logs are designed to grow indefinitely, the natural > response to this design property is log rotation. I don't see how writing logs to stderr solves that problem in any way. Whatever stderr is sent to still has a potentially unlimited amount of data to deal with. > But, it's > impossible to reliably rotate a log file. There's always a chance > that during the rotation some log entries will be written to the file > past the point of rotation, but prior to the point where the next logs > volume starts. Not sure I follow you there. You seem to be thinking of a particular way of rotating log files, where an external process tries to swap the program's log file out from under it without its knowledge. That could be vulnerable to race conditions. But if the program doing the logging handles the rotation itself, there's no reason it has to lose data. -- Greg

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Re: FileNotFoundError thrown due to file name in file, rather than file itself
by Loris Bennett 12 নভেম্বর, 2024

12 নভেম্বর, 2024

Cameron Simpson <cs(a)cskk.id.au> writes: > On 11Nov2024 18:24, dieter.maurer(a)online.de <dieter.maurer(a)online.de> wrote: >>Loris Bennett wrote at 2024-11-11 15:05 +0100: >>>I have the following in my program: >>> try: >>> logging.config.fileConfig(args.config_file) >>> config = configparser.ConfigParser() >>> config.read(args.config_file) >>> if args.verbose: >>> print(f"Configuration file: {args.config_file}") >>> except FileNotFoundError: >>> print(f"Error: configuration file {args.config_file} not found. Exiting.") >> >>Do not replace full error information (including a traceback) >>with your own reduced error message. >>If you omit your "try ... except FileNotFoundError` >>(or start the `except` clause with a `raise`), you >>will learn where in the code the exception has been raised >>and likely as well what was not found (Python is quite good >>with such error details). > > Actually, file-not-found is pretty well defined - the except action > itself is fine in that regard. > > [...] >>>2. In terms of generating a helpful error message, how should one >>> distinguish between the config file not existing and the log file not >>> existing? > > Generally you should put a try/except around the smallest possible > piece of code. So: > > config = configparser.ConfigParser() > try: > config.read(args.config_file) > except FileNotFoundError as e: > print(f"Error: configuration file {args.config_file} not found: {e}") > > This way you know that the config file was missing. I appreciate the point you make about the smallest possible piece of code, although I can imagine that this could potentially create a lot of try/except clutter and I might just want a single block and then try to catch various exceptions. Regarding your example above, if 'missingfile.py' contains the following import configparser config = configparser.ConfigParser() try: config.read('/foo/bar') except FileNotFoundError as e: print(f"Error: configuration file {config_file} not found: {e}") them python3 missingfile.py does not produce an any output for me and so does not seem to be a reliable way of handling the case where the config file does not exist. Cheers, Loris -- This signature is currently under constuction.

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FileNotFoundError thrown due to file name in file, rather than file itself
by Loris Bennett 12 নভেম্বর, 2024

12 নভেম্বর, 2024

Hi, I have the following in my program: try: logging.config.fileConfig(args.config_file) config = configparser.ConfigParser() config.read(args.config_file) if args.verbose: print(f"Configuration file: {args.config_file}") except FileNotFoundError: print(f"Error: configuration file {args.config_file} not found. Exiting.") sys.exit(0) and when I ran the program I got the error Error: configuration file /usr/local/etc/sc_mailer not found. Exiting. However, this file *does* exist and *can* be read. By checking the 'filename' attribute of the exception I discovered that the problem was the log file defined *in* the config file, namely [handler_fileHandler] class=FileHandler level=DEBUG formatter=defaultFormatter args=('/var/log/my_prog.log', 'a') This log file did not exist. The exception is thrown by logging.config.fileConfig(args.config_file) My questions are: 1. Should I be surprised by this behaviour? 2. In terms of generating a helpful error message, how should one distinguish between the config file not existing and the log file not existing? Cheers, Loris -- This signature is currently under constuction.

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Re: FileNotFoundError thrown due to file name in file, rather than file itself
by Loris Bennett 12 নভেম্বর, 2024

12 নভেম্বর, 2024

Chris Angelico <rosuav(a)gmail.com> writes: > On Tue, 12 Nov 2024 at 01:59, Loris Bennett via Python-list > <python-list(a)python.org> wrote: >> 2. In terms of generating a helpful error message, how should one >> distinguish between the config file not existing and the log file not >> existing? > > By looking at the exception's attributes rather than assuming and > hard-coding the path in your message? Or, even better, just let the > exception bubble. I didn't consider letting the exception bubble as is the top of the code for a CLI program. I was hoping to just catch what I thought might be a common error of the config file being missing. -- This signature is currently under constuction.

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