Mailman 3 February 2022 - Python-ideas

PEP 671 (late-bound arg defaults), next round of discussion!
by Chris Angelico July 23, 2023

July 23, 2023

I've just updated PEP 671 https://www.python.org/dev/peps/pep-0671/ with some additional information about the reference implementation, and some clarifications elsewhere. *PEP 671: Syntax for late-bound function argument defaults* Questions, for you all: 1) If this feature existed in Python 3.11 exactly as described, would you use it? 2) Independently: Is the syntactic distinction between "=" and "=>" a cognitive burden? (It's absolutely valid to say "yes" and "yes", and feel free to … [View More]

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zip(x, y, z, strict=True)
by Ram Rachum Dec. 1, 2022

Dec. 1, 2022

Here's something that would have saved me some debugging yesterday: >>> zipped = zip(x, y, z, strict=True) I suggest that `strict=True` would ensure that all the iterables have been exhausted, raising an exception otherwise. This is useful in cases where you're assuming that the iterables all have the same lengths. When your assumption is wrong, you currently just get a shorter result, and it could take you a while to figure out why it's happening. What do you think?

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disallow assignment to unknown ssl.SSLContext attributes
by Thomas Grainger June 10, 2022

June 10, 2022

I was debugging some code that was using TLSv1.2 when I expected it to only support TLSv1.3, I tracked it down to a call to: context.miunimum_version = ssl.TLSVersion.TLSv1_3 it should have been: context.minimum_version = ssl.TLSVersion.TLSv1_3 I'd like invalid attribute assignment to be prevented at runtime

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Regex timeouts
by J.B. Langston March 21, 2022

March 21, 2022

Hello, I had opened this bug because I had a bad regex in my code that was causing python to hang in the regex evaluation: https://bugs.python.org/issue46627. I have fixed the problem with that specific regex, but more generally I think it would be good to have a timeout option that could be configurable when compiling the regex so that if the regex didn't complete within the specified timeframe, it would abort and throw an exception. The bug was closed as Won't Fix and it was suggested that … [View More]

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repeat until
by lynneandallan＠optusnet.com.au March 2, 2022

March 2, 2022

Has anyone considered the idea of adding a "do at least once" loop to Python? This is frequently referred to as a do ... while or repeat ... until. At the moment, it's a bit of a hack to achieve this in that we do a 'while True: ( do thing ; if cond: ( break ) )'. Since I don't know how to format these messages, I've used '{' for line-beak-and-indent, ')' for line-break-and-dedent, and ';' for line-break-keeping-same-indent-level. My initial thoughts are that it would be reasonably easy to … [View More]

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Bringing the print statement back
by Guido van Rossum March 2, 2022

March 2, 2022

In Python 3.10 we will no longer be burdened by the old parser (though 3rd party tooling needs to catch up). One thing that the PEG parser makes possible in about 20 lines of code is something not entirely different from the old print statement. I have a prototype: Python 3.10.0a0 (heads/print-statement-dirty:5ed19fcc1a, Jun 9 2020, 16:31:17) [Clang 11.0.0 (clang-1100.0.33.8)] on darwin Type "help", "copyright", "credits" or "license" for more information. Cannot read termcap database; using … [View More]dumb terminal settings. >>> print 2+2 4 >>> print "hello world" hello world >>> print "hello", input("Name:") Name:Guido hello Guido >>> print 1, 2, 3, sep=", " 1, 2, 3 >>> But wait, there's more! The same syntax will make it possible to call *any* function: >>> len "abc" 3 >>> Or any method: >>> import sys >>> sys.getrefcount "abc" 24 >>> Really, *any* method: >>> class C: ... def foo(self, arg): print arg ... >>> C().foo 2+2 4 >>> There are downsides too, though. For example, you can't call a method without arguments: >>> print <built-in function print> >>> Worse, the first argument cannot start with a parenthesis or bracket: >>> print (1, 2, 3) 1 2 3 >>> C().foo (1, 2, 3) Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: C.foo() takes 2 positional arguments but 4 were given >>> print (2+2), 42 4 (None, 42) >>> C().foo [0] Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: 'method' object is not subscriptable >>> No, it's not April 1st. I am seriously proposing this (but I'll withdraw it if the response is a resounding "boo, hiss"). After all, we currently have a bunch of complexity in the parser just to give a helpful error message to people used to Python 2's print statement: >>> print 1, 2, 3 File "<stdin>", line 1 print 1, 2, 3 ^ SyntaxError: Missing parentheses in call to 'print'. Did you mean print(1, 2, 3)? >>> And IIRC there have been a number of aborted attempts at syntactic hacks to allow people to call functions (like print) without parentheses, although (I think) none of them made it into a PEP. The PEG parser makes this much simpler, because it can simply backtrack -- by placing the grammar rule for this syntax (tentatively called "call statement") last in the list of alternatives for "small statement" we ensure that everything that's a valid expression statement (including print() calls) is still an expression statement with exactly the same meaning, while still allowing parameter-less function calls, without lexical hacks. (There is no code in my prototype that checks for a space after 'print' -- it just checks that there's a name, number or string following a name, which is never legal syntax.) One possible extension I didn't pursue (yet -- dare me!) is to allow parameter-less calls inside other expressions. For example, my prototype does not support things like this: >>> a = (len "abc") File "<stdin>", line 1 a = (len "abc") ^ SyntaxError: invalid syntax >>> I think that strikes a reasonable balance between usability and reduced detection of common errors. I could also dial it back a bit, e.g. maybe it's too much to allow 'C().foo x' and we should only allow dotted names (sufficient to access functions in imported modules and method calls on variables). Or maybe we should only allow simple names (allowing 'len x' but disallowing 'sys.getrefcount x'. Or maybe we should really only bring back print statements. I believe there are some other languages that support a similar grammar (Ruby? R? Raku?) but I haven't investigated. Thoughts? -- --Guido van Rossum (python.org/~guido) *Pronouns: he/him **(why is my pronoun here?)* <http://feministing.com/2015/02/03/how-using-they-as-a-singular-pronoun-can-…> [View Less]

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Re: Make 10**400 / 1e200 work?
by Tim Peters Feb. 26, 2022

Feb. 26, 2022

[Tim] > >>> cmath.phase(complex(0.0, 0.0)) > 0.0 > >>> cmath.phase(complex(-0.0, 0.0)) > 3.141592653589793 > >>> cmath.phase(complex(0.0, -0.0)) > -0.0 > >>> cmath.phase(complex(-0.0, -0.0)) > -3.141592653589793 [Marco Sulla <Marco.Sulla.Python(a)gmail.com>] > Whoa. I'm quite curious about why. ... There's no compelling reason to be had. They just made stuff up. In this case, it's apparently motivated by "OK, if the … [View More]

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Make 10**400 / 1e200 work?
by Stefan Pochmann Feb. 24, 2022

Feb. 24, 2022

It crashes because it tries to convert 10**400 to a float and that fails: >>> 10**400 / 1e200 Traceback (most recent call last): File "<pyshell#10>", line 1, in <module> 10**400 / 1e200 OverflowError: int too large to convert to float But with two ints it succeeds: >>> 10**400 / 10**200 1e+200 Note that 1e200 is an integer: >>> 1e200.is_integer() True So that could losslessly be converted to int, and then the division would succeed: >>&… [View More]

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Str to Byte
by one last Day Feb. 24, 2022

Feb. 24, 2022

bit = "\xd8\xa3\xd9\x88\xd9\x87 \xd8\xa8\xd8\xaf\xd9\x8a\xd9\x84 \xd9\x85\xd9\x86 \xd9\x82\xd9\x88\xd9\x84\xd8\xaa\xd9\x8a \xd9\x88\xd8\xa7\xd9\x87\xd8\xa7" # here it is a byte but in str encode_bit = bytes(bit , "latin-1") # i can here say to the computer it is byte #then it will print the same words in but byte print(encode_bit) decode = encode_bit.decode() # and i can then decode it and get what i want print( decode ) bit = open("ss.txt","r") bit = bit.read() # but here i read the file … [View More]

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Using "Get Satisfaction" for Python Suggestions
by Samuel Muldoon Feb. 22, 2022

Feb. 22, 2022

*More than ten years ago, a video game known as "Minecraft" was in its beta testing-phase.**End-users had many suggestions for Minecraft.* *The Mojang team (developers of Minecraft ) used a web platform for suggested changes to the videogame. **The website was known as "Get Satisfaction" **The GetSatisfaction page for Minecraft as so easy to use that sometimes children posted bug reports for Minecraft. Also, several less tenable thoughts fielded by people of the same mental maturity were … [View More]

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CLI convenience?
by Eliot Lear Feb. 21, 2022

Feb. 21, 2022

Hi everyone, I'm sure there's a clear answer, probably written some place obvious, but I wonder if there is a reason why certain functions are not linked to console_scripts. In particular I would think this would be good for json.tool (though I might call it something else, like pyjson_pp). Same with venv. I'm sure I'm missing something obvious. Thanks, Eliot

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A memory map based data persistence and startup speedup approach
by 严懿宸(文极) Feb. 20, 2022

Feb. 20, 2022

Hi folks, as illustrated in faster-cpython#150 [1], we have implemented a mechanism that supports data persistence of a subset of python date types with mmap, therefore can reduce package import time by caching code object. This could be seen as a more eager pyc format, as they are for the same purpose, but our approach try to avoid [de]serialization. Therefore, we get a speedup in overall python startup by ~15%. Currently, we’ve made it a third-party library and have been working on open-… [View More]sourcing. Our implementation (whose non-official name is “pycds”) mainly contains two parts: importlib hooks, this implements the mechanism to dump code objects to an archive and a `Finder` that supports loading code object from mapped memory. Dumping and loading (subset of) python types with mmap. In this part, we deal with 1) ASLR by patching `ob_type` fields; 2) hash seed randomization by supporting only basic types who don’t have hash-based layout (i.e. dict is not supported); 3) interned string by re-interning strings while loading mmap archive and so on. After pycds has been installed, complete workflow of our approach includes three parts: Record name of imported packages to heap.lst, `PYCDSMODE=TRACE PYCDSLIST=heap.lst python run.py` Dump memory archive of code objects of imported packages, this step does not involve the python script, `PYCDSMODE=DUMP PYCDSLIST=heap.lst PYCDSARCHIVE=heap.img python` Run other python processes with created archive, `PYCDSMODE=SHARE PYCDSARCHIVE=heap.img python run.py` We could even make use of immortal objects if PEP 683 [2] was accepted, that could gives CDS more performance improvements. Currently, any archived object is virtually immortal, we add rc by 1 to who has been copied to the archive to avoid being deallocated. However, without changes to CPython, rc fields of archived object will still be updated, therefore have extra footprint due to CoW. More background and detail implementation could be found at [1]. We think it could be an effective way to improve python’s startup performance, and could even do more like sharing large data between python instances. We’re welcome for suggestions and questions. Best, Yichen Yan Alibaba Compiler Group [1] “Faster startup -- Share code objects from memory-mapped file”, https://github.com/faster-cpython/ideas/discussions/150 [2] PEP 683: "Immortal Objects, Using a Fixed Refcount" (draft), https://mail.python.org/archives/list/python-dev@python.org/message/TPLEYDC… [View Less]

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Please consider making dataclasses define an empty __post_init__
by Neil Girdhar Feb. 20, 2022

Feb. 20, 2022

This was discussed here: https://bugs.python.org/issue46757 This came up because I had a dataclass subclass to flax.linen.Module that had its own post-init. When I figured out that I needed to call super, I did so. Later, when I refactored my code to remove the superclass, the super-call was broken. It have been much simpler to always call super in __post_init__ from the start. The proposal on the bug report was to get in the habit of doing: if hasattr(super(), "__post_init__"): … [View More]

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Requirements.txt inside virtual environment
by Vishesh Mangla Feb. 20, 2022

Feb. 20, 2022

Consider the following scenario: 1) You have to format your pc. 2) You copy your python projects to your hard disk along with the virtual environment(I keep the virtual environment in the project folder only). 3)When you copy your projects back after successfully formatting your pc, the useless virtualenv lies there and you can't get the requirements.txt now and have to install all packages one by one. It could be great if pip or python or anyone would by default store a requirements.txt file … [View More]

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Creating ranges with ellipsis
by Soni L. Feb. 18, 2022

Feb. 18, 2022

This might be a silly idea but, would it be a good idea to have ...[a:b:c] return a range(a, b, c)?

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Adding a thin wrapper class around the functions in stdlib.heapq
by bunslow Feb. 17, 2022

Feb. 17, 2022

Nothing so bombastic this time. The heapq functions are basically all named "heapsomething", and basically all take a "heap" for their first argument, with supplementary args coming after. It's a textbook example of the (hypothetical) Object Oriented Manifesto™ where defining a class increases type safety and programmers' conceptual clarity. There're practically no drawbacks, and the code to be added would be very simple. Updating the tests and docs would probably be harder. In pure Python, … [View More]

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Regex pattern matching
by Valentin Berlier Feb. 17, 2022

Feb. 17, 2022

Hi, I've been thinking that it would be nice if regex match objects could be deconstructed with pattern matching. For example, a simple .obj parser could use it like this: match re.match(r"(v|f) (\d+) (\d+) (\d+)", line): case ["v", x, y, z]: print("Handle vertex") case ["f", a, b, c]: print("Handle face") Sequence patterns would extract groups directly. Mapping patterns could be used to extract named groups, which would be nice for simple parsers/… [View More]

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Re: Creating a class template file generator inside Python language
by Avanish Gupta Feb. 16, 2022

Feb. 16, 2022

Thanks for the previous mail. I would like to highlight the value my thought offers to the developers. They often have to write classes while writing a module. In the class, they are supposed to write classes and objects. In a class, typically the attributes are private, and we have getters and setters to access and modify them. My thought is to automate the process of creating such class files with command line. For this, I have made my initial attempt to create a module that does so. Here is … [View More]a short video in which I am demonstrating it. I am also attaching the details of my terminal to get a bit of more details. I am looking forward to hearing from you if I should work on integrating it within the Python Language features, or I should go some other way round, or this is not a very useful tool for many people. *avanishcodes@avanishcodes*:*~*$ echo "No Student.py file here" No Student.py file here*avanishcodes@avanishcodes*:*~*$ ls*Academics* *Documents* *node_modules* *Pictures* *snap* *Videos**bin* *Downloads* package.json *Projects* Student.py*Desktop* *Music* package-lock.json *Public* *Templates**avanishcodes@avanishcodes*:*~*$ rm Student.py *avanishcodes@avanishcodes*:*~*$ ls*Academics* *Documents* *node_modules* *Pictures* *snap**bin* *Downloads* package.json *Projects* *Templates**Desktop* *Music* package-lock.json *Public* *Videos**avanishcodes@avanishcodes*:*~*$ pip install classgen Requirement already satisfied: classgen in ./.local/lib/python3.8/site-packages (0.0.7)*avanishcodes@avanishcodes*:*~*$ python3 -m classgen Student member1,member2,member3,member4,member5,member6 Class Student generated successfully.*avanishcodes@avanishcodes*:*~*$ cat Student.py #(class) Student class Student: """ This class is used to represent a Student. Attributes: member1: The member1 of the Student. member2: The member2 of the Student. member3: The member3 of the Student. member4: The member4 of the Student. member5: The member5 of the Student. member6: The member6 of the Student. Methods: get_member1(self): Gets the member1 of the Student. get_member2(self): Gets the member2 of the Student. get_member3(self): Gets the member3 of the Student. get_member4(self): Gets the member4 of the Student. get_member5(self): Gets the member5 of the Student. get_member6(self): Gets the member6 of the Student. set_member1(self, member1): Sets the member1 of the Student. set_member2(self, member2): Sets the member2 of the Student. set_member3(self, member3): Sets the member3 of the Student. set_member4(self, member4): Sets the member4 of the Student. set_member5(self, member5): Sets the member5 of the Student. set_member6(self, member6): Sets the member6 of the Student. """ _member1: None _member2: None _member3: None _member4: None _member5: None _member6: None def __init__(self, member1, member2, member3, member4, member5, member6): """ Initializes a Student object. Params: member1: The member1 of the Student. member2: The member2 of the Student. member3: The member3 of the Student. member4: The member4 of the Student. member5: The member5 of the Student. member6: The member6 of the Student. """ self._member1 = member1 self._member2 = member2 self._member3 = member3 self._member4 = member4 self._member5 = member5 self._member6 = member6 def get_member1(self): """ Gets the member1 of the Student. Returns: get_member1: The member1 of the Student. """ return self._member1 def get_member2(self): """ Gets the member2 of the Student. Returns: get_member2: The member2 of the Student. """ return self._member2 def get_member3(self): """ Gets the member3 of the Student. Returns: get_member3: The member3 of the Student. """ return self._member3 def get_member4(self): """ Gets the member4 of the Student. Returns: get_member4: The member4 of the Student. """ return self._member4 def get_member5(self): """ Gets the member5 of the Student. Returns: get_member5: The member5 of the Student. """ return self._member5 def get_member6(self): """ Gets the member6 of the Student. Returns: get_member6: The member6 of the Student. """ return self._member6 def set_member1(self, member1): """ Sets the member1 of the Student. Params: member1: The member1 of the Student. """ self._member1 = member1 def set_member2(self, member2): """ Sets the member2 of the Student. Params: member2: The member2 of the Student. """ self._member2 = member2 def set_member3(self, member3): """ Sets the member3 of the Student. Params: member3: The member3 of the Student. """ self._member3 = member3 def set_member4(self, member4): """ Sets the member4 of the Student. Params: member4: The member4 of the Student. """ self._member4 = member4 def set_member5(self, member5): """ Sets the member5 of the Student. Params: member5: The member5 of the Student. """ self._member5 = member5 def set_member6(self, member6): """ Sets the member6 of the Student. Params: member6: The member6 of the Student. """ self._member6 = member6 *avanishcodes@avanishcodes*:*~*$ AvanishCodes - VMware Workstation 16 Player (No... <https://drive.google.com/file/d/1I4rbwjr-l5eNqbNzpnY8QOGrXP-c3t_B/view?usp=…> Thanks and Regards Avanish On Mon, Feb 14, 2022 at 4:59 AM Avanish Gupta <avanishcodes(a)gmail.com> wrote: > Hi all > I am Avanish, a junior from Indian Institute of Information Technology, > Surat. > I have written a simple script to generate class files based on command > line arguments. It is quite simple in nature, but if improved and packaged > as a part of the Python language feature, it has the potential to save a > lot of time for the developers across the globe. > Please check the package at https://pypi.org/project/classgen > If I can be given a chance to work on it, I would like to do it in much > more detail. I hope I am on the right track, and I seek the guidance of > your expertise and experience. > > > > Thanks and regards > [View Less]

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New convenience attribute pathlib.Path.stems
by Clay Gerrard Feb. 15, 2022

Feb. 15, 2022

>>> from pathlib import Path >>> p = Path('/etc/swift/object.ring.gz') >>> p.suffix '.gz' >>> p.suffixes ['.ring', '.gz'] >>> p.stem 'object.ring' >>> p.stems Traceback (most recent call last): File "<stdin>", line 1, in <module> AttributeError: 'PosixPath' object has no attribute 'stems' I think it would have been nice if .stems = ['object', '.ring'] The idiomatic answer for this persons definition of "true" stem: https://… [View More]

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Please consider mentioning property without setter when an attribute can't be set
by Neil Girdhar Feb. 15, 2022

Feb. 15, 2022

Hello, consider: class C: @property def f(self) -> int: return 2 class D(C): pass D().f = 2 Gives: Traceback (most recent call last): File "/home/neil/src/cmm/a.py", line 10, in <module> D().f = 2 AttributeError: can't set attribute 'f' This can be a pain to debug when the property is buried in a base class. Would it make sense to mention the reason why the attribute can't be set, namely that it's on a property without a setter? Best, Neil

7 11

Missing expandvars equivalent in pathlib
by anthony.flury Feb. 13, 2022

Feb. 13, 2022

All, I know that /os.path/ includes a function /expandvars(..)/ which expands any environment variables in a given path, but from looking at the /pathlib/ documentation It seems there is no equivalent to /os.path.expandvars(..) on any class/ in /pathlib/, and the recommendation seems to be to use /pathlib/ to do any and all path manipulations, with the exception of expanding environment variables. It appears that the recommended /pathlib/ compatible code to fully convert any file path (… [View More]

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Re: Please consider mentioning property without setter when an attribute can't be set
by Bruce Leban Feb. 13, 2022

Feb. 13, 2022

I think the more useful message would be something along the lines of AttributeError: can't set attribute 'f' on object of type 'D' This will help you track down the error. Steven D'Aprano listed three reasons why it might fail which sounds right but frequently the underlying reason is something else: You're trying to set the attribute on the wrong object (e.g., element.color vs. element.style.color). I wish more error messages identified the types of the objects involved. --- Bruce > >

1 0

Mapping unpacking assignment
by Yurii Karabas Feb. 12, 2022

Feb. 12, 2022

I am proposing to add smth like JS destructing assignment to python. Basically, it will allow unpacking any mapping (should have __getitem__ and keys() methods) into variables. Proposed syntax: ``` m = {"a": 1, "b": 2, "c": 3, "d": 4} {a, b} = m # a: 1, b: 2 {a, b, **rest} = m # a: 1, b: 2, rest: {c: 3, d: 4} ``` It will be rawly equal to: ``` m = {"a": 1, "b": 2, "c": 3, "d": 4} # {a, b} = m a = m["a"] b = m["b"] # {a, b, **rest} rest = {**m} a = rest.pop("a") b = rest.pop("b") ``` This … [View More]

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Datetime operation in itertools count
by Aman Pandey Feb. 10, 2022

Feb. 10, 2022

I wanted to generate all the dates between two date ranges for which I was using count function in the itertools and to my surprise count function doesn't support datetime operation. For example >import datetime >from itertools import count >count(datetime.date.today(), datetime.timedelta(1)) Why is count function only limited to numbers shouldn't we make it generic that it should support operation like datetime where addition between the objects is possible. Would like to hear … [View More]

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urllib: addressing inflexibility in scheme-based joining
by Lincoln Auster Feb. 10, 2022

Feb. 10, 2022

Hi, About a month ago, I opened BPO 46337 with regard to urllib's inflexible handling of URL schemes. (Another discussion (from 2013) occured in BPO-18828.) In my ticket, I proposed supplementing the hard-coded uses_* scheme lists that control URL parsing and joining behavior with an enum that may override behavior when calling a function that would effect it. (More detail is available in BPO 46337 and potential code is available in cpython PR#30520.) Do you think this would be a generally … [View More]

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