Mailman 3 August 2018 - Python-ideas

Redefining method
by Jamesie Pic 20 Aug '18

20 Aug '18

Hi all, Not sure if this subject has been brought up already, but why can't we redefine methods as such for example: c = MyClass o = c() def c.foo(cls): ... def o.bar(self): ... Thanks in advance for sharing some of your insight -- ∞

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Re: [Python-ideas] Jump to function as an an alternative to call function
by Jacob Solinsky 18 Aug '18

18 Aug '18

So when getx is executed inside a let form, if it tries to read/write the value of X it interacts with the X entry in the let form's symbol table before moving to find X in the global environment, right? That is similar to what I was trying to accomplish in python, but with the local symbol table of the calling function rather than a let form. I think the way a "jump to" function rather than a "call function" would be implemented would be by removing the prologue and epilogue of the function's compiled code. Something vaguely like this: def foo(a,b): c = bar(d =3)% return c+2 def bar(d) a += 2 e = 4 return a + b + d +e foo(7, 2) Here would be the symbol table Scope Foo __________ a: fp - 1 b: fp - 2 d: fp - 3 e: fp - 5 c: fp - 4 The interpreter would have to recognize that bar was being jumped to rather than called and thus inject bar's arguments and variable declarations and return value (if assigned to) into foo's stack frame. The translation of the above code would be this (I apologize for the strange pseudoassembly, I don't know any of those languages on a more than cursory level. The below code is obviously very slow, each variable read from the memory and written to memory at every step, with no storage of local variables in registers.) The "return c+2" statement is changed from a return into a c += 2 assignment in the calling function. PUSH fp, returnregister # preserve old value in return register PUSH -1(fp), 7 # load a PUSH -2(fp), 2 # load b PUSH -3(fp), 3 # load d PUSH -4(fp), 0 # initialize c ADDI -1(fp), -1(fp), 2 # a += 2 PUSH -5(fp), 4 # load e ADD -4(fp), -1(fp), -2(fp) # c = a + b + d + e ADD -4(fp), -4(fp), -5(fp) # c = a + d + d + e continued ADDI returnregister, -4(fp), 2 # return c + 2 On Thu, 16 Aug 2018, 14:44 Jonathan Fine, <jfine2358(a)gmail.com> wrote: > Hi Jacob > > I'm finding the python-ideas list a bit noisy, so I'm sending this > off-list. > > I've found > > > https://www.gnu.org/software/emacs/manual/html_node/elisp/Dynamic-Binding.h… > > https://www.gnu.org/software/emacs/manual/html_node/elisp/Variable-Scoping.… > > Please confirm that this is at least close to what you want, to be > able to program your problem efficiently. > > Meanwhile, I'm thinking about how your algorithm might be expressed in > Python. > > -- > Jonathan >

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Re: [Python-ideas] Jump to function as an an alternative to call function
by Jacob Solinsky 16 Aug '18

16 Aug '18

On Thu, 16 Aug 2018, 12:44 Jacob Solinsky, <jacobsolinsky(a)gmail.com> wrote: > I wanted the called, jumped to function to change state in the caller. > From what I tried to do, passing locals() cannot accomplish this. I have > made it happen in other languages though. > In the R language, one can do this > > foo = function(){ > localenv = environment() > eval(bar, environment = localenv) > > The above code captures the environment of the calling function and > executes the called function as if the calling function's local environment > was the global environment. bar doesn't have to be a function, it can be > any valid R expression captured with the expr() function, and everything in > R is an expression thus allowing for the full usage code blocks. Outside of > lisp-like languages this feat seems to usually be impossible though. > > > On Thu, 16 Aug 2018, 12:34 Jonathan Fine, <jfine2358(a)gmail.com> wrote: > >> Hi Chris >> >> Steve and you wrote: >> >> >> there >> >> are times where I have really wanted to access the caller's >> environment, >> >> not the environment where my function was defined. >> >> > what am I missing? can't you get that by passing locals() in to a >> function? >> >> I think this will fail when values are changed. According to >> https://docs.python.org/3/library/functions.html#locals >> > The contents of this dictionary should not be modified; changes may not >> affect the values of local and free variables used by the interpreter. >> >> I suspect that Jacob, the original poster, wants to change state, and >> also to read changed state. Jacob, could you confirm or correct, that >> you want the called function to be able to change state in caller (or >> perhaps even further up the stack). >> >> To finish, here's an interactive example of changing the value of >> locals(). >> >> >>> def f(a=1): loc = locals(); yield loc; yield a >> >>> it = f() >> >>> ctx = next(it) >> >>> ctx >> {'a': 1} ## This surprised me. >> >>> >> >>> >> >>> def f(a=1): loc = locals(); yield locals(); yield a >> >>> it = f() >> >>> ctx = next(it) >> >>> ctx >> {'a': 1, 'loc': {...}} >> >>> ctx['a'] = 3 >> >>> ctx['loc']['a'] = 5 >> >>> next(it) ## Is it 1 or 3 or 5? >> 1 ## The value of 'a' hasn't changed. >> >> -- >> Jonathan >> _______________________________________________ >> Python-ideas mailing list >> Python-ideas(a)python.org >> https://mail.python.org/mailman/listinfo/python-ideas >> Code of Conduct: http://python.org/psf/codeofconduct/ >> >

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Python docs page: In what ways is None special
by Jonathan Fine 16 Aug '18

16 Aug '18

This arises out of PEP 505 - None-aware operators. I thought, a page on how None is special would be nice. I've not found such a page on the web. We do have === https://docs.python.org/3/library/constants.html None The sole value of the type NoneType. None is frequently used to represent the absence of a value, as when default arguments are not passed to a function. Assignments to None are illegal and raise a SyntaxError. === So decided to start writing such a page, perhaps to be added to the docs. All code examples in Python3.4. Here's my first attempt. I'm sure I've missed some important examples. Please help, if you can. None is a keyword ============== >>> None = 0 SyntaxError: can't assign to keyword >>> import keyword >>> keyword.kwlist ['False', 'None', 'True', 'and', 'as', 'assert', 'break', 'class', 'continue', 'def', 'del', 'elif', 'else', 'except', 'finally', 'for', 'from', 'global', 'if', 'import', 'in', 'is', 'lambda', 'nonlocal', 'not', 'or', 'pass', 'raise', 'return', 'try', 'while', 'with', 'yield'] The Command Line Interpreter hides None ================================= >>> None >>> None is false in a boolean context ========================== >>> bool(None) False Procedures return None ================== >>> a = [3,1,2] >>> b = a.sort() >>> a, b ([1, 2, 3], None) Dictionary get returns None if not found ============================== >>> {}.get('dne') is None True None is default return value ===================== >>> def fn(): pass ... >>> fn() # No response! >>> print(fn()) # Here's why. None None is used as a sentinel default value ============================== Particularly useful when default value must be determined in body of function. --- def insort_right(a, x, lo=0, hi=None): # ... if hi is None: hi = len(a) --- Thank you for your attention. What have I missed? -- Jonathan

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Hi!
by Marko Ristin-Kaufmann 16 Aug '18

16 Aug '18

Hi, Please let me briefly introduce myself. I'm Marko and live in Zurich, Switzerland. I learned Python and Django during an intership in 2007 and followed its development ever since. I did research in computer vision (at ETH Zurich) and now I work at Parquery AG (Zurich, Switzerland) where we implement most of our infra-structure in Python 3. Cheers, Marko

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Re: [Python-ideas] Python docs: page: In what ways in None special
by Rhodri James 15 Aug '18

15 Aug '18

(Sorry to break threading on this. In a fit of idiocy I deleted the original email before realising I wanted to reply.) First off, thanks for doing this Jonathan. Documentation is usually a thankless task, so we ought to start by thanking you! I have a few comments on both content and style, good and bad. Starting with style, I notice you tend to write in short sentences. This is generally a good thing, but sometimes you make them too short. This gets really visible when you start sentences with "And" or "But"; my old English teacher would have menaced you with a ruler for such bad grammar. You can start a sentence with a conjunction, but it adds extra emphasis that you don't usually want. The start of the "Why None?" section is a good example. It reads like: "Sometimes a value is required. But (pay careful attention to this, it's important and there will be a quiz later) we're not able to provide one." I exaggerate for effect, of course, but it would read more easily as: "Sometimes a value is required but we're not able to provide one." On 'None is a constant': Erm. I think you've got carried away with simplifying this and gone down a blind alley. None is a literal, and like any other literal can't be rebound. Either this entire section is irrelevant or you meant to explain that there is only one "NoneType" object. Constant is a bit of a loaded term in Python, and I think you've fallen foul of it here. On 'None is the default return value': I really dislike the term "falls off the bottom". I can't think of anything similarly short and expressive, but I grimaced when I saw it. The 'list gotcha' is a good example of how None is used as the default return value and why programmers should pay attention, but it doesn't deserve it's own subsection. It's a direct consequence of None being the return value. On 'None can signal failure': Here's where I think None stops being special in the document. None can signal failure. So False, 0, an empty string, a negative number or pretty much anything else. If you want to have a section on how None is used, that great, but having this in the section "How None is special" is just wrong. On 'None as a placeholder default': Ditto. It's common to use None as a placeholder for a mutable type; explaining that common gotcha here would be good. Epigraphs: If you're going to quote Sherman, you need to expand on the uniqueness of None. Not doing that just makes it look irrelevant. It's not irrelevant, it's a tigger [1] [1] Misquoting Michael Flanders from the introduction to "The Hippopotamus Song" on "At The Drop Of A Hat". -- Rhodri James *-* Kynesim Ltd

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Conduct on python-ideas
by Brett Cannon 14 Aug '18

14 Aug '18

I'm starting a new thread on this to make sure it receives appropriate visibility for everyone on this list. *There are ramifications for those involved in this whole situation* as outlined at the end of this email. To review, this mailing list operates under the PSF Community Code of Conduct: https://www.python.org/psf/codeofconduct/ . That means everyone is expected to be open, considerate, and respectful. Titus and I have operated this list such that people who don't follow the CoC get a warning, then a temporary ban of a month or two, then a year-long ban, then a permanent ban (and we reserve the right to skip any of these steps as we see fit based on how bad the infraction was). Since the traffic here can get a bit heavy and thus we don't read every email, we rely on people reporting things as appropriate to python-ideas-owner@ if things have gotten out of hand. And boy did things get out of hand on the "Syntactic sugar to declare partial functions" thread. Here is what I saw play out (bolding is mine): ---------- [Abe] Words like 'partial', 'curry', 'lambda', and 'closure' are fine for text books, published papers, and technical discussion, *but I think they would (or do in the case of 'lambda') harm Python*. [Steven] *That's an extreme overreaction*. Do you mean to imply that there are people who looked at Python, loved the language, but decided to use something else because they didn't like the choice of the keyword "lambda"? If not, in what way is Python harmed? Would it be faster if the keyword was "function", or use less memory, or more expressive? Remember that to millions of programmers in the world, "function" is just as much an obscure foreign piece of jargon they have to memorise as "lambda" is to English-speakers. [Abe] Extreme? I thought it was a rather benign opinion.* I'm not exactly frothing at the mouth here. It's not like I'm declaring holy war on Python for using the word 'lambda'.* I just think it was a mistake (and thatdeath should come to all non-believers). [Steve] You've said that the choice of keyword, "lambda", has caused harm. Given the chance to clarify what you meant, *you stood by your comment that thechoice of keyword "lambda" has done real, significant, non-trivial harm* to Python (the language, or the community). Presumably you fear the same thing will happen again if we choose "partial" (otherwise, why raise the issue?). [Abe] Notice:* I never said "real, significant, non-trivial harm" anywhere* in this entire discussion. I never said anything close to that. *Stop jamming bullshit in my mouth* to suit your narrative that I'm "extremely overreacting". It's not cute. ---------- The way I read this going down is Abe thought something "would harm Python". "Harm" is a strong word to use, so Steven called it an "extreme overreaction". Now stating it like a fact is unnecessary, abrasive, and a bit of hyperbole. Abe thought we he thought and that's fine, but it isn't universally considered an overreaction; it was an opinion and Abe correctly stated it as such. Steven could have easily left out the hyperbole and framing like a statement of fact and still made the same point. Abe then reacted with more hyperbole as he disagreed with Steven's statement that he was overreacting. So now we are reacting to hyperbole with hyperbole. Steven then reacted by overstating the strength of Abe's initial intentions. That's a misunderstanding at best, entirely misleading at worst. At that point Abe crossed a line and basically yelled at Steven to "stop jamming bullshit in [his] mouth". So how should have this been handled? First, dropping all hyperbole, not stating opinions as facts, and not being so abrasive would have probably stopped all of this from happening. Had Steven just said "I think that's an overreaction; can you please clarify what harm you think happened?" then he would have gotten the answer he wanted and Abe would not have taken offense. Abe replying with his own hyperbole didn't help. Steven also didn't need to misrepresent what Abe said. Choosing to re-interpret what level of harm Abe meant was not appropriate (unless Steven got a bit sloppy and replied from memory instead of going back and reading the emails he was replying to). And finally, Abe's response was totally uncalled for. I don't care how out of line someone on this list is, you don't react like that. You come to Titus and me and we will handle it. If you need to, step back for an hour or day before replying if that's what it takes to not react in a rude manner. I shouldn't be having to explain to adults on how to communicate among strangers of different cultures, but here we are. I did an entire PyCon US keynote on why we need to treat open source as a series of kindnesses and react as such: https://youtu.be/tzFWz5fiVKU?t=49m29s . If we don't treat everything as a kindness then open source simply doesn't work and people end up walking way from open source and the Python community. So,* ramifications from all of this* ... Steven, stop stating your opinion as fact and being needlessly abrasive. Your abrasiveness in responses has pushed multiple threads to breaking points like this before and I know you have the skills to not do that if you chose to because I've seen it here and on other mailing lists. Constructive conversations never need anything abrasive in them in order to get your intentions across. Consider this a warning to scale back the tone in response to be more respectful. Abe, you're receiving a warning about how you eventually reacted. In the future please just step away from the keyboard until you can react appropriately. The way you responded to Steven is not acceptable as it isn't respectful to others on this list and there shouldn't be "vigilante responses"; if you feel someone has violated the CoC then tell us admins and we will handle it. -Brett & Titus

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Python Community Code of Conduct
by Jonathan Fine 13 Aug '18

13 Aug '18

https://www.python.org/psf/codeofconduct/ Python Community Code of Conduct The Python community is made up of members from around the globe with a diverse set of skills, personalities, and experiences. It is through these differences that our community experiences great successes and continued growth. When you're working with members of the community, we encourage you to follow these guidelines which help steer our interactions and strive to keep Python a positive, successful, and growing community. A member of the Python community is: Open Members of the community are open to collaboration, whether it's on PEPs, patches, problems, or otherwise. We're receptive to constructive comment and criticism, as the experiences and skill sets of other members contribute to the whole of our efforts. We're accepting of all who wish to take part in our activities, fostering an environment where anyone can participate and everyone can make a difference. Considerate Members of the community are considerate of their peers -- other Python users. We're thoughtful when addressing the efforts of others, keeping in mind that often times the labor was completed simply for the good of the community. We're attentive in our communications, whether in person or online, and we're tactful when approaching differing views. Respectful Members of the community are respectful. We're respectful of others, their positions, their skills, their commitments, and their efforts. We're respectful of the volunteer efforts that permeate the Python community. We're respectful of the processes set forth in the community, and we work within them. When we disagree, we are courteous in raising our issues. Overall, we're good to each other. We contribute to this community not because we have to, but because we want to. If we remember that, these guidelines will come naturally. Questions/comments/reports? Please write to psf(a)python.org. Note: this email address is to all of the PSF Board of Directors and the PSF Staff. Alternatively, you may reach Ewa Jodlowska, Director of Operations, at ewa(a)python.org.

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Consider adding an iterable option to dataclass
by Neil Girdhar 13 Aug '18

13 Aug '18

It would be nice if dataclasses (https://docs.python.org/3/library/dataclasses.html#dataclasses.dataclass) had an option to make them a sequence. This would make dataclass(frozen=True, order=True, sequence=True) an optionally-typed version of namedtuple. It would almost totally supplant it except that namedtuples have a smaller memory footprint. sequence would simply inherit from collections.abc.Sequence and implement the two methods __len__ and __getitme__. Best, Neil

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Is this PEP-able? "with" statement inside genexps / list comprehensions
by Rudy Matela 12 Aug '18

12 Aug '18

Hello, Do you think it would be nice to allow with statements inside genexps or list comprehensions? The functions __enter__ and __exit__ would be automatically called as iterables are traversed. I am thinking of drafting a PEP about this. Examples: This g = (f.read() for fn in filenames with open(fn) as f) would be equivalent to the following use of a generator function: def __gen(): for fn in filenames: with open(fn) as f: yield f.read() g = __gen() This list = [f.read() for fn in filenames with open(fn) as f] would be equivalent to the following: list = [] for fn in filenames: with open(fn) as f: list.append(f.read()) -- Rudy

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