Mailman 3 October 2015 - Python-ideas

Utility to override custom signal handlers
by Demian Brecht Oct. 9, 2015

Oct. 9, 2015

Sometimes it's useful to be able to reset a select number of overridden signal handlers temporarily to allow for default handling. While trivial, might there be use for such a utility existing in the signal module? Something to the effect of: @contextmanager def default_sighandlers(*signums): handlers = [] for signum in signums: handlers.append((signum, signal.getsignal(signum))) signal.signal( signum, signal.SIG_DFL if signum != signal.SIGINT … [View More]

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Binary f-strings
by Eric V. Smith Oct. 8, 2015

Oct. 8, 2015

Now that f-strings are in the 3.6 branch, I'd like to turn my attention to binary f-strings (fb'' or bf''). The idea is that: >>> bf'datestamp:{datetime.datetime.now():%Y%m%d}\r\n' Might be translated as: >>> (b'datestamp:' + ... bytes(format(datetime.datetime.now(), ... str(b'%Y%m%d', 'ascii')), ... 'ascii') + ... b'\r\n') Which would result in: b'datestamp:20150927\r\n' The only real question is: what encoding to use for the second parameter to … [View More]bytes()? Since an object must return unicode from __format__(), I need to convert that to bytes in order to join everything together. But how? Here I suggest 'ascii'. Unfortunately, this would give an error if __format__ returned anything with a char greater than 127. I think we've learned that an API that only raises an exception with certain specific inputs is fragile. Guido has suggested using 'utf-8' as the encoding. That has some appeal, but if we're designing this for wire protocols, not all protocols will be using utf-8. Another idea would be to extend the "conversion char" from just 's', 'r', or 'a', which don't make much sense for bytes, to instead be a string that specifies the encoding. The default could be ascii, and if you want to specify something else: bf'datestamp:{datetime.datetime.now()!utf-8:%Y%m%d}\r\n' That would work for any encoding that doesn't have ':', '{', or '}' in the encoding name. Which seems like a reasonable restriction. And I might be over-generalizing here, but you'd presumably want to make the encoding a non-constant: bf'datestamp:{datetime.datetime.now()!{encoding}:%Y%m%d}\r\n' I think my initial proposal will be to use 'ascii', and not support any conversion characters at all for fb-strings, not even 's', 'r', and 'a'. In the future, if we want to support encodings other than 'ascii', we could then add !conversions mapping to encodings. My reasoning for using 'ascii' is that 'utf-8' could easily be an error for non-utf-8 protocols. And by using 'ascii', at least we'd give a runtime error and not put possibly bogus data into the resulting binary string. Granted, the tradeoff is that we now have a case where whether or not the code raises an exception is dependent upon the values being formatted. If 'ascii' is the default, we could later switch to 'utf-8', but we couldn't go the other way. The only place this is likely to be a problem is when formatting unicode string values. No other built-in type is going to have a non-ascii compatible character in its __format__, unless you do tricky things with datetime format_specs. Of course user-defined types can return any unicode chars from __format__. Once we make a decision, I can apply the same logic to b''.format(), if that's desirable. I'm open to suggestions on this. Thanks for reading. -- Eric. [View Less]

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string.replace should accept a list as a first argument
by Emil Rosendahl Petersen Oct. 7, 2015

Oct. 7, 2015

I think string.replace should be changed accept a list as a first argument. That way, if I had this string: "There are a lot of undesirable people in this filthy world" Then I could do this, replace(['undesirable', 'filthy'], ''), in case that's what I wanted to do. Now, string.replace doesn't accept a list as its first argument, and complains about implicit conversion. Is there any great obstacle to just having the function loop over that list, calling itself in case we get a list … [View More]

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Pre-PEP Adding A Secrets Module To The Standard Library
by Steven D'Aprano Oct. 7, 2015

Oct. 7, 2015

Following on to the discussions about changing the default random number generator, I would like to propose an alternative: adding a secrets module to the standard library. Attached is a draft PEP. Feedback is requested. (I'm going to only be intermittently at the keyboard for the next day or so, so my responses may be rather slow.) -- Steve

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Non-English names in the turtle module (with Spanish example)
by Al Sweigart Oct. 5, 2015

Oct. 5, 2015

I've created a prototype for how we could add foreign language names to the turtle.py module and erase the language barrier for non-English schoolkids. The Tortuga module has the same functionality as You can test it out by running "pip install tortuga" https://pypi.python.org/pypi/Tortuga Since Python 2 doesn't have simpledialog, I used the PyMsgBox pure-python module for the input boxes. This code is small enough that it could be added into turtle.py. (It's just used for simple tkinter … [View More]

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PEP 505 (None coalescing operators) thoughts
by Jeff Hardy Oct. 5, 2015

Oct. 5, 2015

TL;DR: +1 for the idea -1 on the propagating member-access or index operators +1 on spelling it "or?" C# has had null-coalescing since about 2005, and it's one feature I miss in every other language that I use. I view null/None as a necessary evil, so getting rid of them as soon possible is a good thing in my book. Nearly every bit of Python I've ever written would have benefitted from it, if just to get rid of the "x if x is not None else []" mess. That said, I think the other (propagating) … [View More]

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secrets module -- secret.keeper?
by Jim J. Jewett Oct. 3, 2015

Oct. 3, 2015

Will the secrets module offer any building blocks to actually protect a secret? e.g., an easy way to encrypt a file with a given password? an encrypted datastore? a getpass that works even in IDLE? -jJ

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asyncio: factoring-out of the general mechanism
by Christoph Groth Oct. 2, 2015

Oct. 2, 2015

Hello, I have a question/idea about the support for asynchronous programming in Python. With Python 3.5, support for asynchronous programming has been added to the core Python language. The new language features, however, are only useful with an event loop, as provided (only?) by the asyncio stdlib module. I notice that already the class asyncio.AbstractEventLoop contains many things that to me seem very specific to particular applications. For examples that class contains placeholders for … [View More]

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Re: [Python-ideas] Consider making enumerate a sequence if its argument is a sequence
by Brett Cannon Oct. 2, 2015

Oct. 2, 2015

On Wed, 30 Sep 2015 at 09:38 Neil Girdhar <mistersheik(a)gmail.com> wrote: > In fairness, one is a superset of the other. You always get an Iterable. > You sometimes get a Sequence. It's a bit like multiplication? with > integers you get integers, with floats, you get floats. > No, it's not like multiplication. =) I hate saying this since I think it's tossed around too much, but int/float substitution doesn't lead to a Liskov substitution violation like substituting out a … [View More]

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