Mailman 3 April 2012 - Python-ideas

@classproperty, @abc.abstractclasspropery, etc.
by K. Richard Pixley Dec. 16, 2020

Dec. 16, 2020

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 … [View More]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 [View Less]

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Specify number of items to allocate for array.array() constructor
by Sven Rahmann Feb. 22, 2020

Feb. 22, 2020

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 … [View More]

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Yielding through context managers
by Joshua Bartlett Jan. 9, 2013

Jan. 9, 2013

I'd like to propose adding the ability for context managers to catch and handle control passing into and out of them via yield and generator.send() / generator.next(). For instance, class cd(object): def __init__(self, path): self.inner_path = path def __enter__(self): self.outer_path = os.getcwd() os.chdir(self.inner_path) def __exit__(self, exc_type, exc_val, exc_tb): os.chdir(self.outer_path) def __yield__(self): self.inner_path = … [View More]

6 14

i18n and Python tracebacks
by Andre Roberge Oct. 28, 2012

Oct. 28, 2012

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 … [View More]

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Re: [Python-ideas] Cofunctions - Back to Basics
by Mark Shannon Oct. 21, 2012

Oct. 21, 2012

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.… [View More]

9 25

Cofunctions PEP - Revision 4
by Greg Ewing Oct. 13, 2012

Oct. 13, 2012

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 … [View More]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: [View Less]

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Module __getattr__ [Was: breaking out of module execution]
by Jim Jewett May 8, 2012

May 8, 2012

On Wed, Apr 25, 2012 at 2:35 PM, Matt Joiner <anacrolix(a)gmail.com> wrote: > If this is to be done I'd like to see all special methods supported. One of > particular interest to modules is __getattr__... For What It's Worth, supporting __setattr__ and __getattr__ is one of the few reasons that I have considered subclassing modules. The workarounds of either offering public set_varX and get_varX functions, or moving configuration to a separate singleton, just feel kludgy. Since … [View More]

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PEP 4XX: Adding sys.implementation
by Eric Snow May 3, 2012

May 3, 2012

I've written up a PEP for the sys.implementation idea. Feedback is welcome! You'll notice some gaps which I'll be working on to fill in over the next couple days. Don't mind the gaps. <wink> They are in less critical (?) portions and I wanted to get this out to you before the weekend. Thanks! -eric -------------------------------------------------------------- PEP: 4XX Title: Adding sys.implementation Version: $Revision$ Last-Modified: $Date$ Author: Eric Snow <… [View More]ericsnowcurrently(a)gmail.com> Status: Draft Type: Standards Track Content-Type: text/x-rst Created: 26-April-2012 Python-Version: 3.3 Abstract ======== This PEP introduces a new variable for the sys module: ``sys.implementation``. The variable holds consolidated information about the implementation of the running interpreter. Thus ``sys.implementation`` is the source to which the standard library may look for implementation-specific information. The proposal in this PEP is in line with a broader emphasis on making Python friendlier to alternate implementations. It describes the new variable and the constraints on what that variable contains. The PEP also explains some immediate use cases for ``sys.implementation``. Motivation ========== For a number of years now, the distinction between Python-the-language and CPython (the reference implementation) has been growing. Most of this change is due to the emergence of Jython, IronPython, and PyPy as viable alternate implementations of Python. Consider, however, the nearly two decades of CPython-centric Python (i.e. most of its existance). That focus had understandably contributed to quite a few CPython-specific artifacts both in the standard library and exposed in the interpreter. Though the core developers have made an effort in recent years to address this, quite a few of the artifacts remain. Part of the solution is presented in this PEP: a single namespace on which to consolidate implementation specifics. This will help focus efforts to differentiate the implementation specifics from the language. Additionally, it will foster a multiple-implementation mindset. Proposal ======== We will add ``sys.implementation``, in the sys module, as a namespace to contain implementation-specific information. The contents of this namespace will remain fixed during interpreter execution and through the course of an implementation version. This ensures behaviors don't change between versions which depend on variables in ``sys.implementation``. ``sys.implementation`` is a dictionary, as opposed to any form of "named" tuple (a la ``sys.version_info``). This is partly because it doesn't have meaning as a sequence, and partly because it's a potentially more variable data structure. The namespace will contain at least the variables described in the `Required Variables`_ section below. However, implementations are free to add other implementation information there. Some possible extra variables are described in the `Other Possible Variables`_ section. This proposal takes a conservative approach in requiring only two variables. As more become appropriate, they may be added with discretion. Required Variables -------------------- These are variables in ``sys.implementation`` on which the standard library would rely, meaning they would need to be defined: name the name of the implementation (case sensitive). version the version of the implementation, as opposed to the version of the language it implements. This would use a standard format, similar to ``sys.version_info`` (see `Version Format`_). Other Possible Variables ------------------------ These variables could be useful, but don't necessarily have a clear use case presently: cache_tag a string used for the PEP 3147 cache tag (e.g. 'cpython33' for CPython 3.3). The name and version from above could be used to compose this, though an implementation may want something else. However, module caching is not a requirement of implementations, nor is the use of cache tags. repository the implementation's repository URL. repository_revision the revision identifier for the implementation. build_toolchain identifies the tools used to build the interpreter. url (or website) the URL of the implementation's site. site_prefix the preferred site prefix for this implementation. runtime the run-time environment in which the interpreter is running. gc_type the type of garbage collection used. Version Format -------------- XXX same as sys.version_info? Rationale ========= The status quo for implementation-specific information gives us that information in a more fragile, harder to maintain way. It's spread out over different modules or inferred from other information, as we see with ``platform.python_implementation()``. This PEP is the main alternative to that approach. It consolidates the implementation-specific information into a single namespace and makes explicit that which was implicit. With the single-namespace-under-sys so straightforward, no alternatives have been considered for this PEP. Discussion ========== The topic of ``sys.implementation`` came up on the python-ideas list in 2009, where the reception was broadly positive [1]_. I revived the discussion recently while working on a pure-python ``imp.get_tag()`` [2]_. The messages in `issue 14673`_ are also relevant. Use-cases ========= ``platform.python_implementation()`` ------------------------------------ "explicit is better than implicit" The platform module guesses the python implementation by looking for clues in a couple different sys variables [3]_. However, this approach is fragile. Beyond that, it's limited to those implementations that core developers have blessed by special-casing them in the platform module. With ``sys.implementation` the various implementations would *explicitly* set the values in their own version of the sys module. Aside from the guessing, another concern is that the platform module is part of the stdlib, which ideally would minimize implementation details such as would be moved to ``sys.implementation``. Any overlap between ``sys.implementation`` and the platform module would simply defer to ``sys.implementation`` (with the same interface in platform wrapping it). Cache Tag Generation in Frozen Importlib ---------------------------------------- PEP 3147 defined the use of a module cache and cache tags for file names. The importlib bootstrap code, frozen into the Python binary as of 3.3, uses the cache tags during the import process. Part of the project to bootstrap importlib has been to clean out of Lib/import.c any code that did not need to be there. The cache tag defined in Lib/import.c was hard-coded to ``"cpython" MAJOR MINOR`` [4]_. For importlib the options are either hard-coding it in the same way, or guessing the implementation in the same way as does ``platform.python_implementation()``. As long as the hard-coded tag is limited to CPython-specific code, it's livable. However, inasmuch as other Python implementations use the importlib code to work with the module cache, a hard-coded tag would become a problem.. Directly using the platform module in this case is a non-starter. Any module used in the importlib bootstrap must be built-in or frozen, neither of which apply to the platform module. This is the point that led to the recent interest in ``sys.implementation``. Regardless of how the implementation name is gotten, the version to use for the cache tag is more likely to be the implementation version rather than the language version. That implementation version is not readily identified anywhere in the standard library. Implementation-Specific Tests ----------------------------- XXX http://hg.python.org/cpython/file/2f563908ebc5/Lib/test/support.py#l509 http://hg.python.org/cpython/file/2f563908ebc5/Lib/test/support.py#l1246 http://hg.python.org/cpython/file/2f563908ebc5/Lib/test/support.py#l1252 http://hg.python.org/cpython/file/2f563908ebc5/Lib/test/support.py#l1275 Jython's ``os.name`` Hack ------------------------- XXX http://hg.python.org/cpython/file/2f563908ebc5/Lib/test/support.py#l512 Impact on CPython ================= XXX Feedback From Other Python Implementators ========================================= IronPython ---------- XXX Jython ------ XXX PyPy ---- XXX Past Efforts ============ XXX PEP 3139 XXX PEP 399 Open Issues =========== * What are the long-term objectives for sys.implementation? - pull in implementation detail from the main sys namespace and elsewhere (PEP 3137 lite). * Alternatives to the approach dictated by this PEP? * ``sys.implementation`` as a proper namespace rather than a dict. It would be it's own module or an instance of a concrete class. Implementation ============== The implementatation of this PEP is covered in `issue 14673`_. References ========== .. [1] http://mail.python.org/pipermail/python-dev/2009-October/092893.html .. [2] http://mail.python.org/pipermail/python-ideas/2012-April/014878.html .. [3] http://hg.python.org/cpython/file/2f563908ebc5/Lib/platform.py#l1247 .. [4] http://hg.python.org/cpython/file/2f563908ebc5/Python/import.c#l121 .. _issue 14673 http://bugs.python.org/issue14673 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: [View Less]

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argparse FileType v.s default arguments...
by Mike Meyer May 3, 2012

May 3, 2012

While I really like the argparse module, I've run into a case I think it ought to handle that it doesn't. So I'm asking here to see if 1) I've overlooked something, and it can do this, or 2) there's a good reason for it not to do this or maybe 3) this is a bad idea. The usage I ran into looks like this: parser.add_argument('configfile', default='/my/default/config', type=FileType('r'), nargs='?') If I provide the argument, everything works fine, and it opens the named file for me. If … [View More]

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Anyone working on a platform-agnostic os.startfile()
by Hobson Lane April 27, 2012

April 27, 2012

There is significant interest in a cross-platform file-launcher.[1][2][3][4] The ideal implementation would be an operating-system-agnostic interface that launches a file for editing or viewing, similar to the way os.startfile() works for Windows, but generalized to allow caller-specification of view vs. edit preference and support all registered os.name operating systems, not just 'nt'. Mercurial has a mature python implementation for cross-platform launching of an editor (either GUI editor … [View More]

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Re: [Python-ideas] Python-ideas Digest, Vol 65, Issue 43
by Hobson Lane April 27, 2012

April 27, 2012

Formatted and finished Rebert's solution to this issue http://bugs.python.org/issue3177 But the question of where to put it is still open ( shutil.open vs. shutil.launch vs. os.startfile ): 1. `shutil.open()` will break anyone that does `from shutil import *` or edits the shutil.py file and tries to use the builtin open() after the shutil.open() definition. 2. `shutil.launch()` is better than shutil.open() due to reduced breakage, but not as simple or DRY or reverse-compatible as putting it … [View More]in os.startfile() in my mind. This fix just implements the functionality of os.startfile() for non-Windows OSes. 3. `shutil.startfile()` was recommended against by a developer or two on this mailing list, but seems appropriate to me. The only upstream "breakage" for an os.startfile() location that I can think of is the failure to raise exceptions on non-Windows OSes. Any legacy (<3.0) code that relies on os.startfile() exceptions in order to detect a non-windows OS is misguided and needs re-factoring anyway, IMHO. Though their only indication of a "problem" in their code would be the successful launching of a viewer for whatever path they pointed to... 4. `os.launch()` anyone? Not me. On Mon, Apr 23, 2012 at 6:00 PM, <python-ideas-request(a)python.org> wrote: > Send Python-ideas mailing list submissions to > python-ideas(a)python.org > > To subscribe or unsubscribe via the World Wide Web, visit > http://mail.python.org/mailman/listinfo/python-ideas > or, via email, send a message with subject or body 'help' to > python-ideas-request(a)python.org > > You can reach the person managing the list at > python-ideas-owner(a)python.org > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of Python-ideas digest..." > > > Today's Topics: > > 1. Anyone working on a platform-agnostic os.startfile() (Hobson Lane) > 2. Re: Anyone working on a platform-agnostic os.startfile() > (Chris Rebert) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Mon, 23 Apr 2012 13:21:10 +0800 > From: Hobson Lane <hobsonlane(a)gmail.com> > To: python-ideas(a)python.org > Cc: Hobson's Totalgood Aliases <knowledge(a)totalgood.com> > Subject: [Python-ideas] Anyone working on a platform-agnostic > os.startfile() > Message-ID: > <CACZ_DoceeafEpu9wsyG0JPuAGUay0PR91xOZSwzrVy4BGZo1nQ(a)mail.gmail.com > > > Content-Type: text/plain; charset="iso-8859-1" > > There is significant interest in a cross-platform > file-launcher.[1][2][3][4] The ideal implementation would be > an operating-system-agnostic interface that launches a file for editing or > viewing, similar to the way os.startfile() works for Windows, but > generalized to allow caller-specification of view vs. edit preference and > support all registered os.name operating systems, not just 'nt'. > > Mercurial has a mature python implementation for cross-platform launching > of an editor (either GUI editor or terminal-based editor like vi).[5][6] > The python std lib os.startfile obviously works for Windows. > > The Mercurial functionality could be rolled into os.startfile() with > additional named parameters for edit or view preference and gui or non-gui > preference. Perhaps that would enable backporting belwo Python 3.x. Or is > there a better place to incorporate this multi-platform file launching > capability? > > [1]: > > http://stackoverflow.com/questions/1856792/intelligently-launching-the-defa… > [2]: > > http://stackoverflow.com/questions/434597/open-document-with-default-applic… > [3]: > > http://stackoverflow.com/questions/1442841/lauch-default-editor-like-webbro… > [4]: > > http://stackoverflow.com/questions/434597/open-document-with-default-applic… > [5]: http://selenic.com/repo/hg-stable/file/2770d03ae49f/mercurial/ui.py > [6]: > http://selenic.com/repo/hg-stable/file/2770d03ae49f/mercurial/util.py > [View Less]

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breaking out of module execution
by Eric Snow April 27, 2012

April 27, 2012

In a function you can use a return statement to break out of execution in the middle of the function. With modules you have no recourse. This is akin to return statements being allowed only at the end of a function. There are a small number of ways you can work around this, but they aren't great. This includes using wrapper modules or import hooks or sometimes from-import-*. Otherwise, if your module's execution is conditional, you end up indenting everything inside an if/else statement. … [View More]

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sys.implementation
by Eric Snow April 26, 2012

April 26, 2012

In October 2009 there was a short flurry of interest in adding "sys.implementation" as an object to encapsulate some implementation-specific information [1]. Does anyone recollect where this proposal went? Would anyone object to reviving it (or a variant)? -eric [1] http://mail.python.org/pipermail/python-dev/2009-October/092893.html

7 16

Structured Error Output
by Bryce Boe April 26, 2012

April 26, 2012

Hi, I looked through the man page for python's interpreter and appears that there is no way to properly distinguish between error messages output to stderr by the interpreter and output produced the by a user-program to stderr. What I would really like to have are two things: 1) an option to output interpreter generated messages to a specified file, whether these messages are uncatchable syntax errors, or catchable runtime errors that result in the termination of the interpreter. This … [View More]

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Haskell envy
by Nestor April 25, 2012

April 25, 2012

The other day a colleague of mine submitted this challenge taken from some website to us coworkers: Have the function ArrayAddition(arr) take the array of numbers stored in arr and print true if any combination of numbers in the array can be added up to equal the largest number in the array, otherwise print false. For example: if arr contains [4, 6, 23, 10, 1, 3] the output should print true because 4 + 6 + 10 + 3 = 23. The array will not be empty, will not contain all the same elements, and … [View More]

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Re: [Python-ideas] Haskell envy (Terry Reedy)
by Hobson Lane April 25, 2012

April 25, 2012

> On 4/22/2012 11:18 PM, Chris Rebert wrote: > > On Sun, Apr 22, 2012 at 7:55 PM, Terry Reedy<tjreedy(a)udel.edu> wrote: > >> On 4/22/2012 9:07 PM, Nestor wrote: > > <snip> > >>> false. For example: if arr contains [4, 6, 23, 10, 1, 3] the output > >>> should print true because 4 + 6 + 10 + 3 = 23. > >> Since the order of the numbers is arbitrary and irrelevant to the > problem, > >> it should be formulated in … [View More]

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Re: [Python-ideas] Have dict().update() return its own reference.
by Xavier Ho April 21, 2012

April 21, 2012

Thanks, that's fair, for consistency. One use case for my question was a stackoverflow question regarding merging two dict's. If update() returned its own reference, and if we explicitly wanted a copy (instead of an in-place modification), we could have used dict(x).update(y) given x and y are both dict() instances. Cheers, Xav On 20 April 2012 22:35, Laurens Van Houtven <_(a)lvh.cc> wrote: > As a general rule, methods/functions in Python either *mutate* or > *return*. (… [View More]

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Have dict().update() return its own reference.
by Xavier Ho April 20, 2012

April 20, 2012

Hello, What's the rationale behind the fact that `dict().update()` return nothing? If it returned the dictionary reference, at least we could chain methods, or assign it to another variable, or pass it into a function, etc.. What's the design decision made behind this? Cheers, Xav

1 0

Providing a guarantee that instances of user-defined classes have distinct identities
by Max Moroz April 19, 2012

April 19, 2012

Suppose I model a game of cards, where suits don't matter. I might find the integer representation of cards (14 for "Ace", 13 for "King", ..., 2 for "2") to be convenient. The deck has 4 copies of each card, which I need to distinguish. I was thinking to model a card as follows: class Card(int): __hash__ = int.__hash__ def __eq__(self, other): return self is other This works precisely as I want (at least in CPython 3.2): x = Card(14) y = Card(14) assert x != y # x and y are two different … [View More]

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Pythonect 0.1.0 Release
by Itzik Kotler April 13, 2012

April 13, 2012

Hi All, I'm pleased to announce the first beta release of Pythonect interpreter. Pythonect is a new, experimental, general-purpose dataflow programming language based on Python. It aims to combine the intuitive feel of shell scripting (and all of its perks like implicit parallelism) with the flexibility and agility of Python. Pythonect interpreter (and reference implementation) is written in Python, and is available under the BSD license. Here's a quick tour of Pythonect: The canonical "… [View More]Hello, world" example program in Pythonect: >>> "Hello World" -> print <MainProcess:Thread-1> : Hello World Hello World >>> '->' and '|' are both Pythonect operators. The pipe operator (i.e. '|') passes one item at a item, while the other operator passes all items at once. Python statements and other None-returning function are acting as a pass-through: >>> "Hello World" -> print -> print <MainProcess:Thread-2> : Hello World <MainProcess:Thread-2> : Hello World Hello World >>> >>> 1 -> import math -> math.log 0.0 >>> Parallelization in Pythonect: >>> "Hello World" -> [ print , print ] <MainProcess:Thread-4> : Hello World <MainProcess:Thread-5> : Hello World ['Hello World', 'Hello World'] >>> range(0,3) -> import math -> math.sqrt [0.0, 1.0, 1.4142135623730951] >>> In the future, I am planning on adding support for multi-processing, and even distributed computing. The '_' identifier allow access to current item: >>> "Hello World" -> [ print , print ] -> _ + " and Python" <MainProcess:Thread-7> : Hello World <MainProcess:Thread-8> : Hello World ['Hello World and Python', 'Hello World and Python'] >>> >>> [ 1 , 2 ] -> _**_ [1, 4] >>> True/False return values as filters: >>> "Hello World" -> _ == "Hello World" -> print <MainProcess:Thread-9> : Hello World >>> >>> "Hello World" -> _ == "Hello World1" -> print False >>> >>> range(1,10) -> _ % 2 == 0 [2, 4, 6, 8] >>> Last but not least, I have also added extra syntax for making remote procedure call easy: >> 1 -> inc@xmlrpc://localhost:8000 -> print <MainProcess:Thread-2> : 2 2 >>> Download Pythonect v0.1.0 from: http://github.com/downloads/ikotler/pythonect/Pythonect-0.1.0.tar.gz More information can be found at: http://www.pythonect.org I will appreciate any input / feedback that you can give me. Also, for those interested in working on the project, I'm actively interested in welcoming and supporting both new developers and new users. Feel free to contact me. Regards, Itzik Kotler | http://www.ikotler.org [View Less]

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in str.replace(old, new), allow 'old' to accept a tuple
by Tshepang Lekhonkhobe April 13, 2012

April 13, 2012

Hi, I find the fact that 'prefix' in str.startswith(prefix) accept a tuple quite useful. That's because one can do a match on more than one pattern at a time, without ugliness. Would it be a good idea to do the same for str.replace(old, new)? before >>> 'foo bar baz'.replace('foo', 'baz').replace('bar', 'baz') baz baz baz after >>> 'foo bar baz'.replace(('foo', 'bar'), 'baz') baz baz baz

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generator.close
by Matt Joiner April 11, 2012

April 11, 2012

Why can't generator.close() return the value if a StopIteration is raised? The PEPs mentioned that it was proposed before, but I can't find any definitive reason, and it's terribly convenient if it does.

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Allow imports to a global name
by Sven Marnach April 11, 2012

April 11, 2012

Sometimes it is useful to do a import to a global name inside a function. A common use case is the 'pylab' module, which must be imported *after* the backend has been set using 'matplotlib.use()'. If the backend is configuration-dependent, the statement import pylab will usually be inside a function, but the module should be available globally, so you would do global pylab import pylab While this code works (at least in CPython), the current language specification forbids it [1]… [View More]

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all, any - why no none ?
by Steven Samuel Cole April 10, 2012

April 10, 2012

hello, i'm aware they've been around for quite a while, but for some reason, i did not have the builtins all(seq) and any(seq) on the radar thus far. when i used them today, i just assumed there was a corresponding none(seq), but was surprised to learn that is not true. why is that ? has this been considered ? discussed ? dismissed ? i did search, but the net being neither case-sensitive nor semantic, the results were off topic. sure, i can do not all or not any or any of these: http://… [View More]

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Re: [Python-ideas] make __closure__ writable
by Mark Shannon April 10, 2012

April 10, 2012

Yury Selivanov wrote: > On 2012-03-16, at 2:57 PM, Yury Selivanov wrote: > >> Decorators can be nested, and what you can do in this case is to >> find the most inner-wrapped function by traversing the '__wrapped__' >> attributes (and check that the function you found is the actual >> original function). After that you can play with its attributes, >> but you can't simply substitute the function object, as the inner >> decorator won't use it. So … [View More]

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