Mailman 3 July 2021 - Python-ideas

writelines2?
by sandhoners123＠gmail.com 14 Jul '21

14 Jul '21

Right now, writelines is a very big misnomer to many python developers, especially beginners who would expect writelines to put new lines at the end of every element in the list My suggestion is to have either a writelines2 or a newline kwarg which does put new lines automatically at the end of every line written

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Deprecation APIs and language tooling
by Sergei Lebedev 13 Jul '21

13 Jul '21

Hi python-ideas, The subject is by no means new nor unique, and in fact has been discussed on python-ideas at least once <https://mail.python.org/archives/list/python-ideas@python.org/thread/OPY3E4…> before as well as in python/mypy#2403 <https://github.com/python/mypy/issues/2403>.. However, to date, there seems to be no standard way of deprecating things declaratively, and ~every major library has its own internal API for that. For example, * numpy.deprecate, * similar decorators in pandas <https://github.com/pandas-dev/pandas/blob/42adb9f80fb6a048995087276eda2a16e…> and TensorFlow <https://github.com/tensorflow/tensorflow/blob/master/tensorflow/python/util…>, * twisted.python.deprecate <https://twistedmatrix.com/documents/current/api/twisted.python.deprecate.ht…>, * warn_about_renamed_method <https://github.com/django/django/blob/ca9872905559026af82000e46cde6f7dedc89…> in Django, * etc etc. The proliferation of deprecation APIs itself is not a problem, but it does make it difficult (if not impossible) for language tooling to consume that deprecation information and help users of these libraries write better code. Imagine, if there was a standard way to flag something as deprecated. That would allow, for example, an IDE or a linter to statically flag a particular usage site as problematic and, assuming such information is available, to suggest an auto-generated fix (see @Deprecated in Kotlin <https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-deprecated/>, for example). What do you think? Is anyone interested in discussing this further and perhaps sketching an API which could work reasonably well for library authors as well as for tooling? Cheers, Sergei

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Re: Deprecation APIs and language tooling
by Blue 12 Jul '21

12 Jul '21

This already exists as `warnings.DeprecationWarning` see the documentation here: https://docs.python.org/3/library/exceptions.html#DeprecationWarning That said, the fact that this is hidden by default [as seen here]( https://docs.python.org/3/library/warnings.html).. > Base category for warnings about deprecated features when those warnings are intended for other Python developers (ignored by default, unless triggered by code in `__main__`). ..makes it almost useless for most. Going back to your original suggestion though, having some decorator similar to NodeJs `util.deprecate` (which only prints the warning once) would be very convenient and much easier detected by editors and linters.

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Pre PEP: Python Literals (was custom strings before)
by Thomas Güttler 11 Jul '21

11 Jul '21

Thank you Guido, Chris, Matt and Richard for your feedback to my last email. Here is an updated version called "Template Literals". I am looking for a core developer who can sponsor this PEP. Please speak up if you want to help me. Regards, Thomas Güttler Source and updates: Pre-PEP 9999 <https://github.com/guettli/peps/blob/master/pep-9999.rst> PEP: 9999 Title: Template Literals Author: Thomas Güttler <info at thomas-guettler.de> Sponsor: TODO Status: Draft Type: Standards Track Content-Type: text/x-rst </dev/peps/pep-0012> Created: 08-Jun-2021 Python-Version: TODO Post-History: 08-Jun-2021 ------------------------------ Contents - Abstract <#abstract> - Motivation <#motivation> - Rationale <#rationale> - Specification <#specification> - Security Implications <#security-implications> - Reference Implementation <#reference-implementation> - Alternative Ideas <#alternative-ideas> - Rejected Ideas <#rejected-ideas> - Open Issues <#open-issues> - References <#references> - Copyright <#copyright> Abstract <#id6> This PEP adds Template Literals to Python. To avoid code injection like XSS or SQL-injection Template Literals can help you to write save Python code. Template Literals provide an easy way to access the local and global variables (like f-strings), so that passing a dictionary to the Template is not necessary. Motivation <#id7> In the context of web development Python can do more than providing REST APIs via http. With the trend to Server-Side-Rendering, we face a fundamental question: How to create HTML with Python? If you use the FrOW pattern (HTML fragments over the wire) [1] <#frow>, then you will be writing small methods returning small HTML fragments. As a developer I want to pass escaped data into template literals to be as simple as possible. Rationale <#id8> Imagine you want to create a small HTML fragment in Python, and return it as HTTP-Response: HttpResponse(f''' <h1>Hi {name}</h1> Your messages: {messages}''') The problem in above example is, that no escaping gets done. In above example "name" and "messages" should be treated differently. The variable "name" should get escaped. For example if the name is "Mary & Bob", the result should be "Mary & Bob". The variable "messages" contains HTML which is already escaped. It should not be escaped again. Most frameworks have a way to do this conditional escaping. For example Django uses conditional_escape() <https://docs.djangoproject.com/en/3.2/ref/utils/#django.utils.html.conditio…> [2] <#id2> With the help of conditional_escape() the above problem could be solved like this: HttpResponse(f''' <h1>Hi {conditional_escape(name)}</h1> Your messages: {conditional_escape(messages)}''') This solution has two drawbacks: 1. It is too verbose. Typing "conditional_escape(...)" again and again is cumbersome. 2. If a conditional_escape() gets forgotten Cross-site scripting attacks could be possible, since malicious users could inject HTML. Specification <#id9> Template Literals use backticks (like JavaScript Template Literals <https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Template_…> [3] <#id4>) Example: name = 'Mary & Bob' messages = `<ul><li>message1</li><li>message2</li></ul>` return HttpResponse(` <h1>Hi {name}</h1> Your messages: {messages} Today: {datetime.date.today()}`) Expressions within curly braces get handled liked in f-strings (PEP-498). The Template Literal creates an instance of the new class types.TemplateLiteral. types.TemplateLiteral has two attributes: - template: The raw string inside the backticks. - tokens: A list of tuples: (value, is_literal). For above example this would mean: template = ''' <h1>Hi {name}</h1> Your messages: {messages} Today: {datetime.date.today()}''' tokens = [ ('\n <h1>Hi ', True), ('Mary & Bob', False), ('</h1>\n Your messages: ', True), (<TemplateLiteral "<ul><li>message1</li><li>message2</li></ul>">, False), ('\n\n Today: ', True), (<datetime.date(2021, 6, 9)>, False) ] It is outside this PEP how a consumer of TemplateLiteral handles this data structure. For example the Django web framework could transform a TemplateLiteral to a SafeString like this: def template_literal_to_safestring(template_literal): return mark_safe( ''.join( [ conditional_escape(value) if not is_literal else value for (value, is_literal) in template_literal.tokens ] ) ) This PEP is not related or constraint to the Django framework. It is even not related to HTML. It can be used for any kind of templating. Security Implications <#id10> Template Literals can execute arbitrary code (like f-strings). Template Literals get created by Python developers, not by users. If you want to make templates available for users (for example if you develop a CMS), then please use a different solution. Reference Implementation <#id11> TODO Alternative Ideas <#id12> Instead of backticks for example t'...' could be used. Rejected Ideas <#id13> TODO Open Issues <#id14> TODO References <#id15> [1] <#id1> FrOW, "HTML Fragments Over the Wire". Frameworks like Unpoly, Hotwire or htmx. [2] <#id3> https://docs.djangoproject.com/en/3.2/ref/utils/#django.utils.html.conditio… [3] <#id5> https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Template_… Copyright <#id16> This document is placed in the public domain or under the CC0-1.0-Universal license, whichever is more permissive.

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pathlib.Path(...).json() (again)
by Thomas Grainger 10 Jul '21

10 Jul '21

It's been brought up a few times eg: https://github.com/python/cpython/pull/12465 but I really think it's time to be re-considered. Specifically I love being able to use `asyncio.to_thread(pathlib.Path(...).read_text, encoding="utf8")` It does exactly the right thing for me! It's great because it interacts with the event loop as few times as possible and uses only the RAM absolutely required. I'm looking to be able to do something like `asyncio.to_thread(pathlib.Path(...).json)` defined as: ```python def json(self): import json with self.open("rb") as f: return json.load(f) ``` while this may seem simple to implement in my own code it handles a lot of stuff for me!, Specifically PEP 538, minimal interactions with the asyncio waker pipe, the minimal amount of ram, etc etc. You might ask - if json why not .html() and .xml() and .csv() ? Well each of these formats require specific configuration - eg do you want defused or regular exploding xml? Do you want excel style CSV or GNU style CSV? AFAIK json is the only format with a one shot zeroconf bytes -> structure format, and so makes it worthy of the pathlib shortcut.

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Default List .get Method
by Austin Graham 07 Jul '21

07 Jul '21

I'm a lurker on this list and wanted to submit my own idea. It's a feature I've been wanting in Python for a while, and I have a simple implementation for it for personal use at the moment. Wanted to get feedback before I move forward. Essentially, I want to be able to perform a simple default get on a list if an index does not exist, similar to a dictionary. For example: *my_dict = {"test1": "value1"}* *my_dict.get("test2", None)* results in a "None" value, since the key doesn't exist. Similarly with a list: *my_list = [1, 2, 3]* *my_list.get(10, 0)* says that since index 10 does not exist, I expect a 0 to be returned. Currently, you have to check the length of the list of use a try/except, which takes more lines than I'd like to use. I'm welcoming feedback on this feature, or if it's already been discussed then I'm expecting to be shut down. Thank you for your time!

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CACHEDIR.TAG for __pycache__ on Linux
by adigitoleo (Leon) 02 Jul '21

02 Jul '21

Hello, I have a small suggestion to make about the generation of the `__pycache__` directory. Would it be possible to also generate a `CACHEDIR.TAG` file in this directory when running Python on Linux? The file is (informally?) specified at <https://bford.info/cachedir/>. This would allow `__pycache__` to be automatically excluded by various Linux tools such as `tar` (using the `--exclude-caches-all` flag). Cheers, Leon

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