Mailman 3 December 2011 - Python-ideas

@classproperty, @abc.abstractclasspropery, etc.
by K. Richard Pixley 16 Dec '20

16 Dec '20

There's a whole matrix of these and I'm wondering why the matrix is currently sparse rather than implementing them all. Or rather, why we can't stack them as: class foo(object): @classmethod @property def bar(cls, ...): ... Essentially the permutation are, I think: {'unadorned'|abc.abstract}{'normal'|static|class}{method|property|non-callable attribute}. concreteness implicit first arg type name comments {unadorned} {unadorned} method def foo(): exists now {unadorned} {unadorned} property @property exists now {unadorned} {unadorned} non-callable attribute x = 2 exists now {unadorned} static method @staticmethod exists now {unadorned} static property @staticproperty proposing {unadorned} static non-callable attribute {degenerate case - variables don't have arguments} unnecessary {unadorned} class method @classmethod exists now {unadorned} class property @classproperty or @classmethod;@property proposing {unadorned} class non-callable attribute {degenerate case - variables don't have arguments} unnecessary abc.abstract {unadorned} method @abc.abstractmethod exists now abc.abstract {unadorned} property @abc.abstractproperty exists now abc.abstract {unadorned} non-callable attribute @abc.abstractattribute or @abc.abstract;@attribute proposing abc.abstract static method @abc.abstractstaticmethod exists now abc.abstract static property @abc.staticproperty proposing abc.abstract static non-callable attribute {degenerate case - variables don't have arguments} unnecessary abc.abstract class method @abc.abstractclassmethod exists now abc.abstract class property @abc.abstractclassproperty proposing abc.abstract class non-callable attribute {degenerate case - variables don't have arguments} unnecessary I think the meanings of the new ones are pretty straightforward, but in case they are not... @staticproperty - like @property only without an implicit first argument. Allows the property to be called directly from the class without requiring a throw-away instance. @classproperty - like @property, only the implicit first argument to the method is the class. Allows the property to be called directly from the class without requiring a throw-away instance. @abc.abstractattribute - a simple, non-callable variable that must be overridden in subclasses @abc.abstractstaticproperty - like @abc.abstractproperty only for @staticproperty @abc.abstractclassproperty - like @abc.abstractproperty only for @classproperty --rich

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Specify number of items to allocate for array.array() constructor
by Sven Rahmann 22 Feb '20

22 Feb '20

At the moment, the array module of the standard library allows to create arrays of different numeric types and to initialize them from an iterable (eg, another array). What's missing is the possiblity to specify the final size of the array (number of items), especially for large arrays. I'm thinking of suffix arrays (a text indexing data structure) for large texts, eg the human genome and its reverse complement (about 6 billion characters from the alphabet ACGT). The suffix array is a long int array of the same size (8 bytes per number, so it occupies about 48 GB memory). At the moment I am extending an array in chunks of several million items at a time at a time, which is slow and not elegant. The function below also initializes each item in the array to a given value (0 by default). Is there a reason why there the array.array constructor does not allow to simply specify the number of items that should be allocated? (I do not really care about the contents.) Would this be a worthwhile addition to / modification of the array module? My suggestions is to modify array generation in such a way that you could pass an iterator (as now) as second argument, but if you pass a single integer value, it should be treated as the number of items to allocate. Here is my current workaround (which is slow): def filled_array(typecode, n, value=0, bsize=(1<<22)): """returns a new array with given typecode (eg, "l" for long int, as in the array module) with n entries, initialized to the given value (default 0) """ a = array.array(typecode, [value]*bsize) x = array.array(typecode) r = n while r >= bsize: x.extend(a) r -= bsize x.extend([value]*r) return x

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i18n and Python tracebacks
by Andre Roberge 28 Oct '12

28 Oct '12

I think it would be a good idea if Python tracebacks could be translated into languages other than English - and it would set a good example. For example, using French as my default local language, instead of >>> 1/0 Traceback (most recent call last): File "<stdin>", line 1, in <module> ZeroDivisionError: integer division or modulo by zero I might get something like >>> 1/0 Suivi d'erreur (appel le plus récent en dernier) : Fichier "<stdin>", à la ligne 1, dans <module> ZeroDivisionError: division entière ou modulo par zéro André

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Re: [Python-ideas] Cofunctions - Back to Basics
by Mark Shannon 21 Oct '12

21 Oct '12

Greg Ewing wrote: > Mark Shannon wrote: > >> Why not have proper co-routines, instead of hacked-up generators? > > What do you mean by a "proper coroutine"? > A parallel, non-concurrent, thread of execution. It should be able to transfer control from arbitrary places in execution, not within generators. Stackless provides coroutines. Greenlets are also coroutines (I think). Lua has them, and is implemented in ANSI C, so it can be done portably. See: http://www.jucs.org/jucs_10_7/coroutines_in_lua/de_moura_a_l.pdf (One of the examples in the paper uses coroutines to implement generators, which is obviously not required in Python :) ) Cheers, Mark.

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Cofunctions PEP - Revision 4
by Greg Ewing 13 Oct '12

13 Oct '12

Here's an updated version of the PEP reflecting my recent suggestions on how to eliminate 'codef'. PEP: XXX Title: Cofunctions Version: $Revision$ Last-Modified: $Date$ Author: Gregory Ewing <greg.ewing(a)canterbury.ac.nz> Status: Draft Type: Standards Track Content-Type: text/x-rst Created: 13-Feb-2009 Python-Version: 3.x Post-History: Abstract ======== A syntax is proposed for defining and calling a special type of generator called a 'cofunction'. It is designed to provide a streamlined way of writing generator-based coroutines, and allow the early detection of certain kinds of error that are easily made when writing such code, which otherwise tend to cause hard-to-diagnose symptoms. This proposal builds on the 'yield from' mechanism described in PEP 380, and describes some of the semantics of cofunctions in terms of it. However, it would be possible to define and implement cofunctions independently of PEP 380 if so desired. Specification ============= Cofunction definitions ---------------------- A cofunction is a special kind of generator, distinguished by the presence of the keyword ``cocall`` (defined below) at least once in its body. It may also contain ``yield`` and/or ``yield from`` expressions, which behave as they do in other generators. From the outside, the distinguishing feature of a cofunction is that it cannot be called the same way as an ordinary function. An exception is raised if an ordinary call to a cofunction is attempted. Cocalls ------- Calls from one cofunction to another are made by marking the call with a new keyword ``cocall``. The expression :: cocall f(*args, **kwds) is evaluated by first checking whether the object ``f`` implements a ``__cocall__`` method. If it does, the cocall expression is equivalent to :: yield from f.__cocall__(*args, **kwds) except that the object returned by __cocall__ is expected to be an iterator, so the step of calling iter() on it is skipped. If ``f`` does not have a ``__cocall__`` method, or the ``__cocall__`` method returns ``NotImplemented``, then the cocall expression is treated as an ordinary call, and the ``__call__`` method of ``f`` is invoked. Objects which implement __cocall__ are expected to return an object obeying the iterator protocol. Cofunctions respond to __cocall__ the same way as ordinary generator functions respond to __call__, i.e. by returning a generator-iterator. Certain objects that wrap other callable objects, notably bound methods, will be given __cocall__ implementations that delegate to the underlying object. Grammar ------- The full syntax of a cocall expression is described by the following grammar lines: :: atom: cocall | <existing alternatives for atom> cocall: 'cocall' atom cotrailer* '(' [arglist] ')' cotrailer: '[' subscriptlist ']' | '.' NAME Note that this syntax allows cocalls to methods and elements of sequences or mappings to be expressed naturally. For example, the following are valid: :: y = cocall self.foo(x) y = cocall funcdict[key](x) y = cocall a.b.c[i].d(x) Also note that the final calling parentheses are mandatory, so that for example the following is invalid syntax: :: y = cocall f # INVALID New builtins, attributes and C API functions -------------------------------------------- To facilitate interfacing cofunctions with non-coroutine code, there will be a built-in function ``costart`` whose definition is equivalent to :: def costart(obj, *args, **kwds): try: m = obj.__cocall__ except AttributeError: result = NotImplemented else: result = m(*args, **kwds) if result is NotImplemented: raise TypeError("Object does not support cocall") return result There will also be a corresponding C API function :: PyObject *PyObject_CoCall(PyObject *obj, PyObject *args, PyObject *kwds) It is left unspecified for now whether a cofunction is a distinct type of object or, like a generator function, is simply a specially-marked function instance. If the latter, a read-only boolean attribute ``__iscofunction__`` should be provided to allow testing whether a given function object is a cofunction. Motivation and Rationale ======================== The ``yield from`` syntax is reasonably self-explanatory when used for the purpose of delegating part of the work of a generator to another function. It can also be used to good effect in the implementation of generator-based coroutines, but it reads somewhat awkwardly when used for that purpose, and tends to obscure the true intent of the code. Furthermore, using generators as coroutines is somewhat error-prone. If one forgets to use ``yield from`` when it should have been used, or uses it when it shouldn't have, the symptoms that result can be extremely obscure and confusing. Finally, sometimes there is a need for a function to be a coroutine even though it does not yield anything, and in these cases it is necessary to resort to kludges such as ``if 0: yield`` to force it to be a generator. The ``cocall`` construct address the first issue by making the syntax directly reflect the intent, that is, that the function being called forms part of a coroutine. The second issue is addressed by making it impossible to mix coroutine and non-coroutine code in ways that don't make sense. If the rules are violated, an exception is raised that points out exactly what and where the problem is. Lastly, the need for dummy yields is eliminated by making it possible for a cofunction to call both cofunctions and ordinary functions with the same syntax, so that an ordinary function can be used in place of a cofunction that yields zero times. Record of Discussion ==================== An earlier version of this proposal required a special keyword ``codef`` to be used in place of ``def`` when defining a cofunction, and disallowed calling an ordinary function using ``cocall``. However, it became evident that these features were not necessary, and the ``codef`` keyword was dropped in the interests of minimising the number of new keywords required. The use of a decorator instead of ``codef`` was also suggested, but the current proposal makes this unnecessary as well. It has been questioned whether some combination of decorators and functions could be used instead of a dedicated ``cocall`` syntax. While this might be possible, to achieve equivalent error-detecting power it would be necessary to write cofunction calls as something like :: yield from cocall(f)(args) making them even more verbose and inelegant than an unadorned ``yield from``. It is also not clear whether it is possible to achieve all of the benefits of the cocall syntax using this kind of approach. Prototype Implementation ======================== An implementation of an earlier version of this proposal in the form of patches to Python 3.1.2 can be found here: http://www.cosc.canterbury.ac.nz/greg.ewing/python/generators/cofunctions.h… If this version of the proposal is received favourably, the implementation will be updated to match. Copyright ========= This document has been placed in the public domain. .. Local Variables: mode: indented-text indent-tabs-mode: nil sentence-end-double-space: t fill-column: 70 coding: utf-8 End:

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Re: [Python-ideas] PEP x: Static module/package inspection
by anatoly techtonik 29 Mar '12

29 Mar '12

(reposting this from Google Group once more as the previous post missed Mailing List, because I was not subscribed in Mailman) *Static module/package inspection* Abstract: - static: without execution (as opposed to dynamic) - module/package: .py or __init__.py file - inspection: get an overview of the contents *What should this do?* * * The proposal to add a mechanism to Python interpreter to get an outline of module/package contents without importing or executing module/package. The outline includes names of classes, functions, variables. It also should contain values for variables that could be provided without sophisticated calculations (e.g. a string, integer, but probably not expressions as it may lead to security leaks). *Why?* * * *user story PEPx.001:* As a Python package maintainer, I find it bothersome to repeatedly write bolierplate code (e.g. setup.py) to package my single file module. The reason I should write setup.py is to provide version and description info. This info is already available in my module source code. So I need to either copy/paste the info from the module manually, or to import (and hence execute) my module during packaging and installation, which I don't want either, because modules are often installed with root privileges. With this PEP, packing tool will be able to extract meta information from my module without executing it or without me manually copying version fields into some 'package configuration file'. *user story PEPx.002:* As a Python Application developer, I find it really complicated to provide plugin extension subsystem for my users. Users need a mechanism to switch between different versions of the plugin, and this mechanism is usually provided by external tool such as setuptools to manage and install multiple versions of plugins in local Python package repository. It is rather hard to create an alternative approach, because you are forced to maintain external meta-data about your plugin modules even in case it is already available inside the module. With this PEP, Python Application will be able to inspect meta-data embedded inside of plugins before choosing which version to load. This will also provide a standard mechanism for applications to check modules returned by packaging tools without executing them. This will greatly simplify writing and debugging custom plugins loaders on different platforms. *Feedback goal* At this stage I'd like to a community response to two separate questions: 1. If everybody feels this functionality will be useful for Python 2. If the solution is technically feasible

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Idea: Google Groups web interface for Ideas
by anatoly techtonik 04 Jan '12

04 Jan '12

As you may know, the python-ideas list is opened only to subscribers. This is inconvenient, because: 1. it requires three step subscription process 2. it is impossible to post a reply to existing thread/idea There is a web-interface in Google Groups at https://groups.google.com/forum/#!forum/python-ideas that can solve problems above and provide some more nifty features such as embedded search. But there comes another problem that messages posted through the group doesn't end in list, because list requires subscription. I've already tried to find a solution, but run out of time, so I summarized the proposal at http://wiki.python.org/moin/MailmanWithGoogleGroups I may or may not be able to publish outcomes of my research, so it would be nice to get some help in investigating the problem and publishing a solution on aforementioned wiki page. Thanks.

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Re: [Python-ideas] [Python-Dev] hello, new dict addition for new eve ?
by julien tayon 04 Jan '12

04 Jan '12

Hello, I had tough time finding a connection to internet :) @Arnaud + Terry Thx, code corrected to have the right terminology. at least my code really test for the good rules :) But being precise matter, so that I changed all the terms to fit in. @nathan << is a symbol indicating an asymetry for left and right value, and I carefully tried to have a symetrical behaviour with left & right : associativity, distribution, commutativity. The whole point about using a symbol, is that it follow rules. That is the reason why consistent_addition class is all about testing linear algebraic rules (hopefully the right way, and now, I hope with the right terminology). But I have reason to think that there are more than way to do addition. Linear algebrae is the most used and intuitive one for non developer, and developer think of sets operations as more intuitive. I guess, it all come down to one point. Which is what is a dict as a mathematical object. If there is more than one choice, which has the most benefits. Should there be more than one definition ? @Guido & Eric In my book there are rules for sets. The question is a dict the same as a vector or as a set ? since sets are using logical operators for operations that are roughly sets operations why not use & ^ | for sets operation on dict ? it would be pretty consistent with sets operations. ( @jakkob ) In this case I would expect inconsistencies error when doing dict( a = 1 ) | dict( a = 2 , b = 2 ) (thus key-> value are seen like an atomic element of the set, unless a "value collision" operator is given, and this collision operator would recursively and naturely apply to the descendants) because I expect both a | b == b | a and a + b = b + a The problem would be indeed list + list vectorish behaviour is my prefered of course. but if we shift the record algebrae addition to another symbol (let's assume << ) we resolve the conflict. But then we have a problem of retro compatibility. We then may be tempted to use & | ^ (since it would be used for dict) and then we have a problem : should [ 1 , 2 ] & [ 3 , 2 ] mean set addition or applying & to all the element of the same rank ? I'm pretty stucked myself in trying to be consistent. Just for the record, why dit you not use "." (dot) for concatenation ? I know it is typographically unreadable on a messy screen, but is there a better reason ? @terry & Nathan Regarding Counter. on https://github.com/jul/ADictAdd_iction/blob/master/demonstrate.py#L120 you may notice that I do have all the property of counter, but counter does not as -this dict- aggregate values and (sub) totals at the same time. It is very convenient for map reduce since it does some re-reduce operations at reduce time. smart, no ? <:o) @terry Sorry for making assertive and carefree statements regarding strong resentment. My bad. @bruce, truth is aim at similarity cosinus for dict, and I imagine a map reduce on dict representing values of a model you want ideal = dict( blue = 1 , height = 180, weight = 70, wage = 500 ) in the filter before the map reduce you would want to filter all records close to this one by using similarity cosinus in this way : filter( lambda model : cos( ideal, model) > .7 , all_model ) http://en.wikipedia.org/wiki/Cosine_similarity of course I will try to advocate dot product, and metrics. As a result my real goal is to make people consider dict as vectors of path to value => value not sets of key => value To solve issues such as weighted decisions and non linear choices (based on trigger or a value belonging to a set) I can fairly easily concevie a projector (which would be a class transforming a vector in a vector, but not with a a matrix, but with computed rules ). @Mark Jansen +1 are you telepath ? Yes a key collision operator would be nice : given for instance an apache log, I will have segments of path, and I may want keys to be the accumulated graph of a user on a website. so my collision rule might be : (key being the referer value the page visited afterwards) dict( a = b, a = c ) + dict( b = e ) = dict( a = dict( b = e ), a = c) I thought of it, but I really loved the conservation rule. And I feared people would think of it as too complicated. Keep It Simple I learnt :) @all Wrapping everything to logicial sense. I was thinking of supersets of object (thus out of the stdlib) that would have different algebrae and could be used as casts on object to redifine + - * / cos & | ^ and for different objects would behave consistently ex : vector( dict ) vector( list ) vector( string ) would make dict & list & string behave like vectors thus mainly supporting elementwise operations sets( dict ) , sets( string ) ... would make dict string be sets of elements ... (with the original dict addition design of GvR et al) Each superset would have a unit test for the operation verifying that behaviour is consistent. (associativity, distributivity, ...) what about this solution ? -- Friendly jul

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Re: [Python-ideas] [Python-Dev] hello, new dict addition for new eve ?
by Guido van Rossum 31 Dec '11

31 Dec '11

On Sat, Dec 31, 2011 at 2:16 AM, julien tayon <julien(a)tayon.net> wrote: > Dear All :) > > 2011/12/30 Eric Snow <ericsnowcurrently(a)gmail.com>: > > On Fri, Dec 30, 2011 at 10:02 AM, Guido van Rossum <guido(a)python.org> > wrote: > >> What I meant is similar to set union on the keys, where if a key exists > in > >> both dicts, the value in the result is equal to one of the values in the > >> operands (and if the value is the same for both operands, that value is > also > >> the result value). > > > > +1 > > > > This is the one I was thinking of too. > > > Well, since I have coded way too much in Perl, my altered sense of > reality has come to a concept I may be introducing too early which is > : algebrae. > > strings, lists, ... have a record algebrae. > ndarray, accudict have a linear algebrae > sets ... have sets algebrae. > > And much more algebrae exists wich all exists not only in my > imagination, but also in math (wich I quite dislike). (Abelian > stuff/Group/matrix/hilbert) > All of these algebrae are consistent as long as any object in the > chain of algebrae are following the same rules. > > And each of these are very legitimate (even though of course my dict > addition is the best without trying to be obnoxious). > > > I was kind of thinking of > 1) giving a property to object called .. __algebrae__, > 2) and through some magic being able to change the algebrae of an > object on the fly. > > My twisted sense of reality inherited from Perl (but a little less > than my math books) tells me There Is More Than One Way To > Consistently Add/Mul/Div/Sub It. > > > As a Proof of Concept I could deliver a monkeypatching of list() that > makes it behave like an numpy array. > Please don't present this in terms of modifications of existing functions/types/methods. Please use subclasses, new modules, new functions, etc. > But, at first I wish to concentrate on dict addition, since I can only > steal a few hours connectivity per day ... So I will try to answer to > everyone since I saw some spoilers of what I had hidden in my mind :) > > Cheers > Thanks > -- --Guido van Rossum (python.org/~guido)

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Re: [Python-ideas] [Python-Dev] hello, new dict addition for new eve ?
by Guido van Rossum 30 Dec '11

30 Dec '11

Hi Julien, Don't despair! I have tried to get people to warm up to dict addition too -- in fact it was my counter-proposal at the time when we were considering adding sets to the language. I will look at your proposal, but I have a point of order first: this should be discussed on python-ideas, not on python-dev. I have added python-ideas to the thread and moved python-dev to Bcc, so followups will hopefully all go to python-ideas. --Guido On Fri, Dec 30, 2011 at 7:26 AM, julien tayon <julien(a)tayon.net> wrote: > Hello, > Sorry to annoy the very busy core devs :) out of the blue > > I quite noticed people were > 1) wanting to have a new dict for Xmas > 2) strongly resenting dict addition. > > Even though I am not a good developper, I have come to a definition of > addition that would follow algebraic rules, and not something of a > dutch logic. (it is a jest, not a troll) > > I propose the following code to validate my point of view regarding > the dictionnatry addition as a proof of concept : > https://github.com/jul/ADictAdd_iction/blob/master/test.py > > It follows all my dusty math books regarding addition + it has the > amability to have rules of conservation. > > I pretty much see a real advantage in this behaviour in functional > programming (map/reduce). (see the demonstrate.py), and it has a sense > (if dict can be seen has vectors). > > I have been told to be a troll, but I am pretty serious. > > Since, I coded with luck, no internet, intuition, and a complete > ignorance of the real meaning of the magic methods most of the time, > thus the actual implementation of the addition surely needs a complete > refactoring. > > Sheers, > Bonne fêtes > Julien > _______________________________________________ > Python-Dev mailing list > Python-Dev(a)python.org > http://mail.python.org/mailman/listinfo/python-dev > Unsubscribe: > http://mail.python.org/mailman/options/python-dev/guido%40python.org > -- --Guido van Rossum (python.org/~guido)

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