Mailman 3 June 2017 - Python-ideas

Run length encoding
by Neal Fultz June 19, 2017

June 19, 2017

Hello python-ideas, I am very new to this, but on a different forum and after a couple conversations, I really wished Python came with run-length encoding built-in; after all, it ships with zip, which is much more complicated :) The general idea is to be able to go back and forth between two representations of a sequence: [1,1,1,1,2,3,4,4,3,3,3] and [(1, 4), (2, 1), (3, 1), (4, 2), (3, 3)] where the first element is the data element, and the second is how many times it is repeated. I … [View More]

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ImportError raised for a circular import
by Barry Scott June 19, 2017

June 19, 2017

Recently I fell into the trap of creating a circular import and yet again it took time to figure out what was wrong. I'm wondering why the python import code does not detect this error and raise an exception. I took a look at the code and got as far as figuring out that I would need to add the detection to the python 3 import code. Unless I missed something I cannot get the detection without modifying the core code as I could see no way to hook the process cleanly. Is it reasonable idea to … [View More]

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Continuation of `__name__` or a builtin function for general name getting
by Alireza Rafiei June 19, 2017

June 19, 2017

Hi all, I'm not sure whether this idea has been discussed before or not, so I apologize in advanced if that's the case. Consider the behavior: >>> f = lambda: True > >>> f.__name__ > '<lambda>' > >>> x = f > >>> x.__name__ > '<lambda>' I'm arguing the behavior above is too brittle/limited and, considering that the name of the attribute is `__name__`, not entirely consistent with Python's AST. Consider: >>> f = lambda: … [View More]

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Make functools.singledispatch register method return original function.
by Mital Ashok June 18, 2017

June 18, 2017

Right now, an example for single dispatch would be: from functools import singledispatch @singledispatch def fun(arg, verbose=True): if verbose: print("Let me just say,", end=" ") print(arg) @fun.register(int) def _(arg, verbose=True): if verbose: print("Strength in numbers, eh?", end=" ") print(arg) @fun.register(list) def _(arg, verbose=True): if verbose: print("Enumerate this:") for i, elem in enumerate(arg): print(i, elem) But … [View More]

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Re: [Python-ideas] [Python-Dev] Language proposal: variable assignment in functional context
by Erik June 16, 2017

June 16, 2017

[cross-posted to python-ideas] Hi Robert, On 16/06/17 12:32, Robert Vanden Eynde wrote: > Hello, I would like to propose an idea for the language but I don't know > where I can talk about it. Can you please explain what the problem is that you are trying to solve? > In a nutshell, I would like to be able to write: > y = (b+2 for b = a + 1) The above is (almost) equivalent to: y = (a+1)+2 I realize the parentheses are not required, but I've included them because if your … [View More]

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Define __fspath__() for NamedTemporaryFile and TemporaryDirectory
by Antoine Pietri June 16, 2017

June 16, 2017

Hello everyone! A very common pattern when dealing with temporary files is code like this: with tempfile.TemporaryDirectory() as tmpdir: tmp_path = tmpdir.name os.chmod(tmp_path) os.foobar(tmp_path) open(tmp_path).read(barquux) PEP 519 (https://www.python.org/dev/peps/pep-0519/) introduced the concept of "path-like objects", objects that define a __fspath__() method. Most of the standard library has been adapted so that the functions accept path-like … [View More]

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Allow function to return multiple values
by joannah nanjekye June 9, 2017

June 9, 2017

Hello Team, I am Joannah. I am currently working on a book on python compatibility and publishing it with apress. I have worked with python for a while we are talking about four years. Today I was writing an example snippet for the book and needed to write a function that returns two values something like this: def return_multiplevalues(num1, num2): return num1, num2 I noticed that this actually returns a tuple of the values which I did not want in the first place.I wanted python to … [View More]

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Re: [Python-ideas] Dictionary destructing and unpacking.
by C Anthony Risinger June 7, 2017

June 7, 2017

On Jun 7, 2017 5:42 PM, "C Anthony Risinger" <c(a)anthonyrisinger.com> wrote: On Jun 7, 2017 5:15 PM, "Matt Gilson" <matt(a)getpattern.com> wrote: On Wed, Jun 7, 2017 at 3:11 PM, Erik <python(a)lucidity.plus.com> wrote: > On 07/06/17 19:14, Nick Humrich wrote: > >> a, b, c = mydict.unpack('a', 'b', 'c') >> > > def retrieve(mapping, *keys): > return (mapping[key] for key in keys) > > > Or even: from operator import itemgetter … [View More]

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π = math.pi
by Mikhail V June 7, 2017

June 7, 2017

Greg Ewing wrote: >Steven D'Aprano wrote: >> There's not much, if any, benefit to writing: >> >> ∫(expression, lower_limit, upper_limit, name) >More generally, there's a kind of culture clash between mathematical >notation and programming notation. Mathematical notation tends to >almost exclusively use single-character names, relying on different >fonts and alphabets, and superscripts and subscripts, to get a large >enough set of identifiers. Whereas in … [View More]

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Improved exception messages
by Chris Angelico June 6, 2017

June 6, 2017

A question came up on python-list regarding the message given when you call float(""). It's somewhat unclear due to the way humans tend to ignore a lack of content: >>> float("spam") Traceback (most recent call last): File "<stdin>", line 1, in <module> ValueError: could not convert string to float: 'spam' >>> float("") Traceback (most recent call last): File "<stdin>", line 1, in <module> ValueError: could not convert string to float: Firstly, is … [View More]

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Security: remove "." from sys.path?
by Victor Stinner June 6, 2017

June 6, 2017

Hi, Perl 5.26 succeeded to remove the current working directory from the default include path (our Python sys.path): https://metacpan.org/pod/release/XSAWYERX/perl-5.26.0/pod/perldelta.pod#Rem… Would it technically possible to make this change in Python? Or would it destroy the world? Sorry, it's a naive question (but honestly, I don't know the answer.) My main use case for "." in sys.path is to be to run an application without installing it: run ./hachoir-metadata which loads the Python "… [View More]

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π = math.pi
by Serhiy Storchaka June 5, 2017

June 5, 2017

What you are think about adding Unicode aliases for some mathematic names in the math module? ;-) math.π = math.pi math.τ = math.tau math.Γ = math.gamma math.ℯ = math.e Unfortunately we can't use ∞, ∑ and √ as identifiers. :-(

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Defer Statement
by Daniel Bershatsky June 4, 2017

June 4, 2017

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Re: [Python-ideas] π = math.pi
by David Mertz June 1, 2017

June 1, 2017

It's awfully easy to add in your own code. Since they are simply aliases, I don't see why bother put the duplication in the standard library. You can even monkey patch if you want it in the 'math' namespace. I'd prefer a bare 'π' in my own code though. On May 31, 2017 11:48 PM, "Serhiy Storchaka" <storchaka(a)gmail.com> wrote: What you are think about adding Unicode aliases for some mathematic names in the math module? ;-) math.π = math.pi math.τ = math.tau math.Γ = math.gamma math.ℯ = … [View More]

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SealedMock proposal for unittest.mock
by Mario Corchero June 1, 2017

June 1, 2017

Hello Everyone! First time writing to python-ideas. *Overview* Add a new mock class within the mock module <https://github.com/python/cpython/blob/master/Lib/unittest/mock.py>, SealedMock (or RestrictedMock) that allows to restrict in a dynamic and recursive way the addition of attributes to it. The new class just defines a special attribute "sealed" which once set to True the behaviour of automatically creating mocks is blocked, as well as for all its "submocks". See sealedmock <… [View More]

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