Mailman 3 February 2018 - Python-ideas

List the methods of a metaclass in the help of its instances
by Yahya Abou 'Imran Feb. 11, 2018

Feb. 11, 2018

For example, in the help of ABCs, the register method witch is defined in ABCMeta is not listed. It's a little bit weird, since it's accessible from the class just like any classmethod or staticmethod, and it's a real feature of the class. I think it would be great if there was sections in the help that look like: | ---------------------------------------------------------------------- | Metaclass methods defined in <TheMetaclass>: | ---------------------------------------------------… [View More]

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Easing set-up of of console python applications
by Mario Corchero Feb. 10, 2018

Feb. 10, 2018

Hello All! I got asked how to configure the logging stack to be able to output directly to console using both stdout and stderr and I could not really find a great answer as adding both as StreamHandlers will result in error and above messages going to stdout. The usecase is having a cli or app that wants to log to console as other tools. Errors and bove to stderr and normal information to stdout. I know the recommended way in Python is to just use print on simple scripts, but it can happen … [View More]

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Consider generalizing Decimal to support arbitrary radix
by Neil Girdhar Feb. 8, 2018

Feb. 8, 2018

Arbitrary radix comes up every now and then and Decimal already has a radix() method. It would be nice when initializing a Decimal object to be able to specify an arbitrary radix>=2.

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Re: [Python-ideas] Complicate str methods
by Franklin? Lee Feb. 8, 2018

Feb. 8, 2018

On Feb 8, 2018 13:06, "Serhiy Storchaka" <storchaka(a)gmail.com> wrote: 08.02.18 12:45, Franklin? Lee пише: > Could it be that re uses an optimization that can also be used in str? > CPython uses a modified Boyer-Moore for str.find: > https://github.com/python/cpython/blob/master/Objects/string > lib/fastsearch.h > http://effbot.org/zone/stringlib.htm > Maybe there's a minimum length after which it's better to precompute a > table. > Yes, there is a special … [View More]

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Re: [Python-ideas] Complicate str methods
by Franklin? Lee Feb. 8, 2018

Feb. 8, 2018

On Thu, Feb 8, 2018 at 11:24 AM, Steve Dower <steve.dower(a)python.org> wrote: > Easily fixed by installing one of the alternate regex libraries. MRAB's regex library, the most prominent alternative, does not use the linear-time search algorithm. The only libraries I know that do are the ones with re2, though I haven't looked deeply. Let it be known that I tried to install pyre2 (re2 on PyPI) on Ubuntu For Windows for the tests, and after hours of no success, I decided that the … [View More]

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Consider making Decimal's context use PEP 567
by Neil Girdhar Feb. 7, 2018

Feb. 7, 2018

Decimal could just pull its Context object from a context variable rather than having to pass it in to all functions. This would be similar to how numpy works.

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Re: [Python-ideas] Possible Enhancement to py Launcher - set default
by Paul Moore Feb. 7, 2018

Feb. 7, 2018

On 7 February 2018 at 19:35, Steve Dower <steve.dower(a)python.org> wrote: > Checking the Version (!=SysVersion) property should be enough (and perhaps > we need to set it properly on install). The launcher currently only works > with PythonCore entries anyway, so no need to worry about other distros. Fair enough. But there was a separate proposal to make the launcher handle non-PythonCore cases - there's a risk of conflicting feature requests here :-) > PEP 514 allows for … [View More]

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Possible Enhancement to py Launcher - set default
by Steve Barnes Feb. 7, 2018

Feb. 7, 2018

When a new version of python is in alpha/beta it is often desirable to have it installed for tests but remain on a previous version for day to day use. However, currently the Windows py launcher defaults to the highest version that it finds, which means that unless you are very careful you will end up having to explicitly specify your older version every time that you start python with it once you have installed the newer version. I an thinking that it would be relatively simple to … [View More]

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Support WHATWG versions of legacy encodings
by Rob Speer Feb. 6, 2018

Feb. 6, 2018

Hi! I joined this list because I'm interested in filling a gap in Python's standard library, relating to text encodings. There is an encoding with no name of its own. It's supported by every current web browser and standardized by WHATWG. It's so prevalent that if you ask a Web browser to decode "iso-8859-1" or "windows-1252", you will get this encoding _instead_. It is probably the second or third most common text encoding in the world. And Python doesn't quite support it. You can see the … [View More]character table for this encoding at: https://encoding.spec.whatwg.org/index-windows-1252.txt For the sake of discussion, let's call this encoding "web-1252". WHATWG calls it "windows-1252", but notice that it's subtly different from Python's "windows-1252" encoding. Python's windows-1252 has bytes that are undefined: >>> b'\x90'.decode('windows-1252') UnicodeDecodeError: 'charmap' codec can't decode byte 0x90 in position 0: character maps to <undefined> In web-1252, the bytes that are undefined according to windows-1252 map to the control characters in those positions in iso-8859-1 -- that is, the Unicode codepoints with the same number as the byte. In web-1252, b'\x90' would decode as '\u0090'. This may seem like a silly encoding that encourages doing horrible things with text. That's pretty much the case. But there's a reason every Web browser implements it: - It's compatible with windows-1252 - Any sequence of bytes can be round-tripped through it without losing information It's not just this one encoding. WHATWG's encoding standard ( https://encoding.spec.whatwg.org/) contains modified versions of windows-1250 through windows-1258 and windows-874. Support for these encodings matters to me, in part, because I maintain a Unicode data-cleaning library, "ftfy". One thing it does is to detect and undo encoding/decoding errors that cause mojibake, as long as they're detectible and reversible. Looking at real-world examples of text that has been damaged by mojibake, it's clear that lots of text is transferred through what I'm calling the "web-1252" encoding, in a way that's incompatible with Python's "windows-1252". In order to be able to work with and fix this kind of text, ftfy registers new codecs -- and I implemented this even before I knew that they were standardized in Web browsers. When ftfy is imported, you can decode text as "sloppy-windows-1252" (the name I chose for this encoding), for example. ftfy can tell people a sequence of steps that they can use in the future to fix text that's like the text they provided. Very often, these steps require the sloppy-windows-1252 or sloppy-windows-1251 encoding, which means the steps only work with ftfy imported, even for people who are not using the features of ftfy. Support for these encodings also seems highly relevant to people who use Python for web scraping, as it would be desirable to maximize compatibility with what a Web browser would do. This really seems like it belongs in the standard library instead of being an incidental feature of my library. I know that code in the standard library has "one foot in the grave". I _want_ these legacy encodings to have one foot in the grave. But some of them are extremely common, and Python code should be able to deal with them. Adding these encodings to Python would be straightforward to implement. Does this require a PEP, a pull request, or further discussion? [View Less]

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Format mini-language for lakh and crore
by David Mertz Feb. 1, 2018

Feb. 1, 2018

In South Asia, a different style of digit delimiters for large numbers is used than in Europe, North America, Australia, etc. With some minor spelling differences, the term lakh is used for a hundred-thousand, and it is generally written as '1,00,000'. In turn, a crore is 100 lakh, and is written as '1,00,00,000'. Extending this pattern, larger numbers continue to use two digits in groups (other than the smallest grouping of three digits. So, e.g. 1e12 is written as 10,00,00,00,00,000. It'… [View More]s nice that we now have the optional underscore in numeric literals. So we could write a number as either `12_34_56_78_00_000` or `1_234_567_800_000` depending on what region of the world and which convention was more familiar. However, in *formatting* those numbers, the format mini-language only allows the European convention. So e.g. In [1]: x = 12_34_56_78_00_000 In [2]: "{:,d}".format(x) Out[2]: '1,234,567,800,000' In [3]: f"{x:,d}" Out[3]: '1,234,567,800,000' In order to get Indian number delimiters, you'd have to write a custom formatting function, notwithstanding that something like 1.5 billion people use the three-then-two delimiting convention. I propose that Python should have an additional grouping option, or some other way to specify this grouping convention. Oddly, the '_' grouping symbol is available, even though no one actually uses that grouper outside of programming languages like Python, e.g.: In [4]: f"{x:_d}" Out[4]: '1_234_567_800_000' I guess this is nice for something like round-tripping numbers used in code, but it's not a symbol anyone uses "natively" (I understand why comma or period cannot be used in numeric literals since they mean something else in Python already). I'm not sure what symbol or combination I would recommend, but finding something suitable shouldn't be so hard. Perhaps now that backtick no longer has any other meaning in Python, it could be used since it looks similar to a comma. E.g. in Python 3.8 we might have: >>> f"{x:`d}" '12,34,56,78,00,000' (actually, this probably isn't any parser issue even in Python 2 since it's already inside quotes; but the issue is moot). Or maybe a two character version like: >>> f"{x:2,d}" '12,34,56,78,00,000' Or: >>> f"{x:,,d}" '12,34,56,78,00,000' Even if `2,` was used, that wouldn't preclude giving an additional length descriptor after it. Now we can have: >>> f"{x:,.2f}" '1,234,567,800,000.00' Perhaps in the future this would work: >>> f"{x:2,.2f}" '12,34,56,78,00,000.00' -- Keeping medicines from the bloodstreams of the sick; food from the bellies of the hungry; books from the hands of the uneducated; technology from the underdeveloped; and putting advocates of freedom in prisons. Intellectual property is to the 21st century what the slave trade was to the 16th. [View Less]

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JSON encoding protocol with __json__ dunder method
by Kiss, György Feb. 1, 2018

Feb. 1, 2018

Hi! Most of the classes (even if very simple like datetime.datetime) cannot be serialized to JSON by default. Would it be a good idea for the default json.JSONEncoder to call the __json__ dunder method automatically if the object has one? I can't find anything about why this protocol or PEP doesn't exists yet. Currently almost everyone implements it like this, there are thousands of results on GitHub to this: https://github.com/search?l=Python&q=def+__json__&type=Code&utf8=%E2%… [View More]

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