Mailman 3 August 2020 - Python-ideas

raise TypeError when giving wrong type of argument in functions
by rawmin.rx＠gmail.com 22 Aug '20

22 Aug '20

I wanted to know if there could be TypeError when giving wrong type for arguments in functions (This usually happens when using other module's function) e.g: def sum(nom1: int, nom2: int): nom = nom1 + nom2 return nom print(sum('hello',2)) if you run this code you will get TypeError for line 2 because 'you can only concatenate str (not "int") to str' But what am i saying is can it raise TypeError for line 4 because I gave 'hello' as nom1 and nom1 should be int Now if I want to check arguments types I should use: def sum(nom1: int, nom2: int): if isinstance(nom1, int) and isinstance(nom1, int): nom = nom1 + nom2 return nom else: raise TypeError('nom1 and nom2 should be int') print(sum('hello',2)) But if they can add what am I am i saying it can decrease lines of this function by 50% and also function author should not worry about checking types anymore! (I know I could use 'assert' but I just wanted to write it as simple as possible)

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Re: Custom keywords (from: Decorators for class non function properties)
by Aveheuzed 18 Aug '20

18 Aug '20

> The new `@const` will be added as a hook to the PEG parser. if the PEG > parser finds a `@const`, it will invoke the miniparser of `mykeywords` > module inherent to `@const`. In this case, it will simply transform > `@const a = 1` in `const PyObject* a = PyLong_FromSsize_t((Py_ssize_t) > 1)` Now that is a simple reason why your proposal, while cool and all, is not realistic : Python just doesn't work that way. Your python source code, when interpreted, is *never* turned back to pure C, so you just can't make a keyword translating to C (or Java, or whatever) stuff. The point is, Python's interpreter needs to know every token that can possibly be passed to him (that's not a problem, thanks to the "@", it can recognize custom keywords) *and* know what to do out of it — and all that at the time you compile the Python interpreter. That makes it really hard to add keywords outside the regular Python development cycle, if even possible. You'd need to make a C API for keywords developers, and modify most of the parser to use and allow the use of such and API. Then developing the keyword would need crafting a bit of parser — in C. I can tell you, parsers can get really complicated, especially at the scale of Python, so I don't think many would have the associated knowledge required to do it. In fact, you never propose a keyword alone: you propose a syntax to use it. (think of `as` : `from math import sqrt as root` vs `with open("filename") as file` vs `try...except Exception as e`). How do you tell what happens when the keyword opens a code block, for example ? TL;DR : it would need rewriting Python from scratch, for a feature too complex to be widely used. If you want custom keywords, you can look at ANTLR, or flex/bison, that's what they're for ! (They're generic parsers, allowing you to craft an interpreter for any language you might like.) You will see that these tools, while dead useful, are much too broad for Python. Now on to use cases : I can see two broad use cases to this tool. The first one is including alien (C-, Java-) features in Python. To see why it wouldn't be possible, read above + This is Python we're talking about, if you need some Java-specific features, code in Java ! The second one is replacing a macro, or a function call (I believe it's the same in Python ^^). It's been discussed here already, especially with the case of `print` : `print "foo"` vs `print "foo"`. It could be generalized to any function call... If you want to support that proposal, I'll let you look in the thread archive for the times it was discussed already, and then — why not ? That's easier to implement, as it's just translating to a function call, we wouldn't even need the special "@", and it may add to readability. Regards, Alexis

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Accelerate zlib and gzip libraries with Intel's Storage Acceleration Libraries
by Ruben Vorderman 17 Aug '20

17 Aug '20

Dear python developers, As a bioinformatician I work a lot with gzip-compressed data. Recently I discovered Intel's Storage Acceleration Libraries at https://github.com/intel/isa-l. These people implemented the DEFLATE and INFLATE algorithms in assembly language. As a result it is much faster than zlib. I have posted a few benchmarks in this python bug https://bugs.python.org/issue41566. (I just discovered bugs.python.org is the wrong place for feature requests. I am sorry, I am still learning about the proper way of doing this things, as this is my first feature proposal). The TLDR is that it can speed up compression by 5x while speeding up compression by 3x compared to standard gzip. Isa-l is bsd-3-clause licensed and as such I see no licensing issues when using it in CPython. It is packaged in linux distros already, so I also see no problems in availability. Furthermore the non-Assembly parts are written in C so including from CPython should not pose very big problems. I am willing to write the PEP if more people think it is a good idea to do this. Best regards, Ruben Vorderman

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Tracebacks for C code in Python
by Ram Rachum 16 Aug '20

16 Aug '20

Here's something that's been bugging me for years. I'll suggest something, but since I'm a total newbie about this area, it's possible that everything I'm saying is impossible or doesn't make sense. I'm working with some Pandas code now, and there's an exception because I'm doing something wrong. I get a traceback, but some of the frames are in pyd files (C code I guess?) so I don't see the code for them. This is frustrating, because the exception message isn't that clear, so I would at least like to know what the code was trying to do when it got the exception. Maybe this will give me more hints about what's going wrong. *Would it be possible to have Python tracebacks include code for C code that's called in Python?* I know very little about how the C-to-Python interaction works, and I assume we'd need something complicated like packaging the source code with the binaries in some way that lets Python get the right line of C code to put in the traceback. This can get complicated. Do you think it's possible? Thanks, Ram.

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Syntactic sugar for checking if a variable is an iterable but not a string?
by Marco Sulla 15 Aug '20

15 Aug '20

Many times I want a function parameter that is an iterable but not a string. Usually I do: try: var.__iter__ except AttributeError: # not an iterable else: try: var.isascii except AttributeError: # put yuour code here or from collections.abc import Iterable if isinstance(var, Iterable) and not isinstance(var, str): # put yuour code here The first example uses duck typing but it's more verbose. I use the first method in an home-made utility function. I think it could be interesting to add a syntactic sugar to do this. Maybe a collections.notTextIterable() collections.nonTextIterable() collections.notStrIterable() collections.iterableNotStr() ?

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Re: basic matrix object
by Marco Sulla 14 Aug '20

14 Aug '20

Excuse me, I sent this message from the wrong email address: On Fri, 14 Aug 2020 at 09:24, Steven D'Aprano <steve(a)pearwood.info> wrote: > Tensors generalise matrices to an arbitrary number of > dimensions, 3D and above. > > https://medium.com/@quantumsteinke/whats-the-difference-between-a-matrix-an… > > I have never studied tensors and wouldn't know where to even begin a > tensor library :-) Another big problem with tensors is the covariance and contravariance. Usually in informatic you denote the covariance with the subscript operator, that on paper is written as subscript. Contravariant index on the contrary is a superscript. Not sure how a programming language can easily represent it. Maybe PEP 472 can help here?

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Re: basic matrix object
by Marco Sulla 14 Aug '20

14 Aug '20

LaTeX for example uses the underscore for subscripts and the ^ for the superscript. This is not acceptable, since Python (and almost all languages) uses [] for subscript, and ^ in Python is the XOR logical operator.

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Make start, stop, step properties on islice
by Mathew Elman 13 Aug '20

13 Aug '20

Is there a reason that itertools.islice does not provide its start, stop and step values as attributes, similar to range? This seems like a sensible and useful thing to have, and would also allow islice's to have a __len__. Mathew

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Aside RE: Re: macaddress or networkaddress module
by Steve Barnes 13 Aug '20

13 Aug '20

As an aside I have a perfect example to back up what Paul is saying below. I work for a large corporation where developers are permitted to install python modules on their development machines, (subject to some licence restrictions), but the proxy settings required to get to PyPi vary from user to user, site to site, day to day (sometimes hour to hour) and connection type to connection type, e.g. If you are connected via WiFi you need to use a different proxy to that needed if you are on a wired connection and on a VPN (we have more than one in use) different again. To help with this I have put together a script that will try pip, if it fails will check the current location for pac.pac, get and parse it for proxies, correct a common incompatibility and then try each discovered proxy and if sill none work fall back to a list of common proxies. Once it finds a working setting it advises the user what to use in the current situation. Obviously, since the script is intended to work out how to get to PyPi, I needed to stick 100% to the standard libraries. -----Original Message----- From: Paul Moore <p.f.moore(a)gmail.com> Sent: 06 April 2020 09:11 To: Stephen J. Turnbull <turnbull.stephen.fw(a)u.tsukuba.ac.jp> Cc: Pete Wicken <petewicken(a)gmail.com>; Python-Ideas <python-ideas(a)python.org> Subject: [Python-ideas] Re: macaddress or networkaddress module On Mon, 6 Apr 2020 at 04:14, Stephen J. Turnbull <turnbull.stephen.fw(a)u.tsukuba.ac.jp> wrote: > That's OK for developers on their "own" machines, but I think there > are still a lot of folks who need approval from corporate (though I > haven't heard from Paul Moore on that theme in quite a while, maybe > it's gotten better?) Howdy :-) It's actually got a bit worse, to the point where I don't bother trying to fight the system as much any more, so things have gone quieter because of that :-) But yes, I still believe that there are important use cases for code that only uses the stdlib, and "not being able to get to the internet" is a valid use case that we shouldn't just dismiss. On the other hand, with regard to the comment you were replying to: > Up to around a decade ago, installing third-party libraries > was a huge mess, but nowadays, PyPI works, Python comes with pip > pre-installed, and telling developers they need internet access > when they first start a new project isn’t considered onerous. I think all of that is true. What I think is more important, though, is around things that aren't so much "projects" as "scripts", and that *distributing* such scripts that depend on 3rd party libraries is still problematic. Here, I'm not talking about making full-fledged packages, or py2exe style fully bundled apps, but "here's this monitoring script I wrote, let's ship it across 10 production systems and why don't you try it out on your dev boxes?" There's a *significant* step change in complexity between doing that if the script depends on just the stdlib, versus if it depends on a 3rd party module. And we don't have a really good answer to that yet (zipapps, and tools like shiv that wrap zipapps, are pretty good in practice, but they are not well known or commonly used). Paul _______________________________________________ Python-ideas mailing list -- python-ideas(a)python.org To unsubscribe send an email to python-ideas-leave(a)python.org https://mail.python.org/mailman3/lists/python-ideas.python.org/ Message archived at https://mail.python.org/archives/list/python-ideas@python.org/message/5BN5D… Code of Conduct: http://python.org/psf/codeofconduct/

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default parameter in fuctions to clean up flow
by Peter Moore 12 Aug '20

12 Aug '20

I have had a long standing unanswered question on on stackoverflow: is it possible to pass a function to a default parameter so that you could do in essence things like this. def time_diff(target_time, curr_time= lambda : datetime.now() ): return curr_time - target_time this would be an syntactical improvement over this style where you have if statement to initialize a missing parameter. def time_diff(target_time, curr_time=None): if curr_time == None: curr_time = datetime.datetime.now() return curr_time - target_time

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