Mailman 3 August 2021 - Python-ideas

SyntaxError says: "can't use starred expression here", but its not the same "starred expression" defined in the Language Reference.
by Matsuoka Takuo 18 Aug '21

18 Aug '21

The error mentioned in the title is this. >>> *() File "<stdin>", line 1 SyntaxError: can't use starred expression here According to the Language Reference https://docs.python.org/3/reference/expressions.html#expression-lists it's not really a starred expression. In the context of defining the notion of starred expressiont, it looks like it's called a starred item. I think the message is confusing and should be fixed. I don't know if "starred item" is the right name to be used there, but it's at least documented (in the Reference). Best regards, Takuo

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Re: New 'How to Write a Good Bug Report' Article for Docs
by c.buhtz＠posteo.jp 18 Aug '21

18 Aug '21

Bug Report https://github.com/mdn/content/issues/8036

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slices syntactic sugar
by eloi.rivard＠aquilenet.fr 18 Aug '21

18 Aug '21

Hi. I am working on a kinda-ORM library, which usage often implies to request data within specific ranges: Foobar.search( attr1="foo", attr2=gt(10), attr3=between(42, 50) ) The use of "gt" or "between" methods to describe those operations feels a bit cumbersome (as it is long to write, and you need to import those functions in a lot of files), and I though it could be more pythonic to use slices instead. Foobar.search( attr1="foo", attr2=slice(10), attr3=slice(42, 50) ) I suggest an alternative way to instanciate slices, that would look like this: Foobar.search( attr1="foo", attr2=[10:], attr3=[42:50] ) What do you think?

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Re: Request for help
by Alan Gauld 17 Aug '21

17 Aug '21

On 16/08/2021 16:54, Mebale Tsige Araya wrote: > Is there anybody who can help me, please? Can I run Python codes on > Browser, please? If so could you have any idea how to run my codes on > Browser? Your question could mean several different things. I'll give very brief answers to each below but you will need to give more specific information for more specific answers. 1) Can I embed Python code in an HTML page and have the browser execute it like JavaScript. No. But you can get Python to JavaScript translators or languages that look like Python (CoffeeScript) that are converted to JavaScript by the server. There are at least 2 very old browsers that do run Python internally but they are used by nobody in the realm world! 2) Is there a web site that lets me enter python code without Python being installed on my device? Yes. There are a few sites that present a virtual terminal online that lets you code python inside a browser. The code actually runs on the server but the input and results appear in the browser. The caveat is that they usually have limited support for modules and they don't allow you to install third party add-ons beyond what the site owner has installed (numpy may be there for example) 3) Can I write web site code in Python that will generate web pages that can be seen in a browser? Yes, there are many, many web frameworks for python from the super sophisticated (eg Zope) to substantial but practical for humans (eg Django) to simple ones for quick and dirty developments (eg Flask) And you can use the cgi module in the standard library for very basic web development. If that's not enough or you meant something different then repost with more details, perhaps even describing what you want to do with it. HTH -- Alan G Author of the Learn to Program web site http://www.alan-g.me.uk/ http://www.amazon.com/author/alan_gauld Follow my photo-blog on Flickr at: http://www.flickr.com/photos/alangauldphotos

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Pattern matching in python function headers
by Sam Frances 17 Aug '21

17 Aug '21

Following on from PEP 634, it would be good to be able to have Erlang / Elixir-style pattern matching in function headers. (I don't know what the technical term is for this language feature, but hopefully the examples will clarify.) Here's the obligatory fibonacci example: ``` def fib(0): return 0 def fib(1): return 1 def fib(n): return fib(n-1) + fib(n-2) ``` Or, another example: ``` def allow_entry({"name": "Bob"}): return "Bob is not allowed in ever!" def allow_entry({"name": "Charles", "day": "Tuesday"}): return "It's a Tuesday, so Charles is allowed in." def allow_entry({"name": "Charles", "day": _}): return "Charles is only allowed in on a Tuesday." def allow_entry({"name": name}): return f"Come in {name}, make yourself at home!" ``` Thanks for considering my idea. Kind regards Sam Frances

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PEP idea
by Will Bradley 16 Aug '21

16 Aug '21

Hi all, As of 3.10 (PEP 604) we've gotten syntactical support for a common type operation— namely, typing.Union[Type1, Type2] can now be written as Type1 | Type2 . This is achieved via overriding the __or__ method. I propose the ? symbol as sugar for typing.Optional, so that typing.Optional[MyType] can be written as MyType? . (Yes, this is lifted directly from C#.) Thoughts? Is it unnecessary now that we can write MyType | None as of 3.10? Thanks, Will

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Create a @deprecated decorator (annotation)
by Leonardo Freua 16 Aug '21

16 Aug '21

[Migrating from https://bugs.python.org/issue44701] Would it be interesting to create a @deprecated decorator to avoid adding warnings.warn("deprecation message", DeprecationWarning, stacklevel=2) in methods body? Using the decorator approach to indicate depreciation would make the methods cleaner (leaving only their responsibilities in the body) and would be easier to identify, as the cue would be close to the method signature and not mixed with the logic inside the body. in some cases it will still be necessary to put warnings.warn (..) inside the body of functions/methods because of some message display condition, or we could also express the message display condition in the decorator in @deprecated itself. But it would be interesting to have the possibility of not putting this inside the method body. Even the decorator can come from the notices module. Example: (Before) def check_metadata(self): """Deprecated API.""" warn("distutils.command.register.check_metadata is deprecated, \ use the check command instead", PendingDeprecationWarning) check = self.distribution.get_command_obj('check') check.ensure_finalized() check.strict = self.strict check.restructuredtext = 1 check.run() (after) @deprecated("distutils.command.register.check_metadata is deprecated, \ use the check command instead") def check_metadata(self): """Deprecated API.""" check = self.distribution.get_command_obj('check') check.ensure_finalized() check.strict = self.strict check.restructuredtext = 1 check.run()

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copy-paste code snippets to the python console
by Raymond Bisdorff 16 Aug '21

16 Aug '21

Dear Python developers, It would be helpful, if the following issue with copy-pasting python code-snippets into the standard shell console, could be investigated and corrected. https://stackoverflow.com/questions/2501208/copying-and-pasting-code-into-t… In particular, copying and pasting from sphinx python and pycon code-blocks with copy button (only >>> and ... lines), is at present not generally working due to the "the shell-s de-indent cmd" need for empty lines. See https://digraph3.readthedocs.io/en/latest/index.html Thank you in advance for you attention, Best Regards, Raymond Bisdorff -- Raymond Bisdorff Emeritus Professor of Computer Science and Applied Mathematics University of Luxembourg http://rbisdorff.github.io/

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Re: PEP idea
by Joren Hammudoglu 16 Aug '21

16 Aug '21

See https://www.python.org/dev/peps/pep-0645/

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C API for converting Python integers to/from bytes sequences
by Serhiy Storchaka 11 Aug '21

11 Aug '21

Python integers have arbitrary precision. For serialization and interpolation with other programs and libraries we need to represent them as fixed-width integers (little- and big-endian, signed and unsigned). In Python, we can use struct, array, memoryview and ctypes use for some standard sizes and int methods int.to_bytes and int.from_bytes for non-standard sizes. In C, there is the C API for converting to/from C types long, unsigned long, long long and unsigned long long. For other C types (signed and unsigned char, short, int) we need to use the C API for converting to long, and then truncate to the destination type with checking for overflow. For integers type aliases like pid_t we need to determine their size and signess and use corresponding C API or wrapper. For non-standard integers (e.g. 24-bit), integers wider than long long, and arbitrary precision integers all is much more complicated. There are private C API functions _PyLong_AsByteArray and _PyLong_FromByteArray, but they are for internal use only. I am planning to add public analogs of these private functions, but more powerful and convenient. PyObject *PyLong_FromBytes(const void *buf, Py_ssize_t size, int byteorder, int signed) Py_ssize_t PyLong_AsBytes(PyObject *o, void *buf, Py_ssize_t n, int byteorder, int signed, int *overflow) PyLong_FromBytes() returns the int object. It only fails in case of memory error or incorrect arguments (e.g. buf is NULL). PyLong_AsBytes() writes bytes to the specified buffer, it does not allocate memory. If buf is NULL it returns the minimum size of the buffer for representing the integer. -1 is returned on error. if overflow is NULL, then OverfowError is raised, otherwise *overflow is set to +1 for overflowing the upper limit, -1 for overflowing the lower limit, and 0 for no overflow. Now I have some design questions. 1. How to encode the byte order? a) 1 -- little endian, 0 -- big endian b) 0 -- little endian, 1 -- big endian c) -1 -- little endian, +1 -- big endian, 0 -- native endian. Do we need to reserve some values for mixed endians? 2. How to specify the reduction modulo 2**(8*size) (like in PyLong_AsUnsignedLongMask)? Add yet one flag in PyLong_AsBytes()? Use special value for the signed argument? 0 -- unsigned, 1 -- signed, 2 (or -1) -- modulo. Or use some combination of signed and overflow? 3. How to specify saturation (like in PyNumber_AsSsize_t())? I.e. values less than the lower limit are replaced with the lower limit, values greater than the upper limit are replaced with the upper limit. Same options as for (2): separate flag, encode in signed (but we need two values here) or combination of other parameters. 4. What exact names to use? PyLong_FromByteArray/PyLong_AsByteArray, PyLong_FromBytes/PyLong_AsBytes, PyLong_FromBytes/PyLong_ToBytes?

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