#171 Chilled out Python decorators with PEP 614
Published March 5, 2020
34 min
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    Sponsored by Datadog: pythonbytes.fm/datadog

    Special guest: David Amos

    David #1: PEP 614 – Relaxing Grammar Restrictions on Decorators

    • Python currently requires that all decorators consist of a dotted name, optionally followed by a single call.
      • E.g., can’t use subscripts or chained calls
    • PEP proposes allowing any valid expression.
    • Motivation for limitation is not a technical requirement:
      • “I have a gut feeling about this one. I'm not sure where it comes from, but I have it... So while it would be quite easy to change the syntax in the future, I'd like to stick to the more restricted form unless a real use case is presented where [changing the syntax] would increase readability.”
      • (Guido van Rossom, Source)
    • Use case highlighted by PEP:
      • List of Qt buttons: buttons = [button0, button1, …]
      • Decorator is a method on a class attribute: button.clicked.connect
      • Under current restrictions you can’t do @button[0].clicked.connect
      • Workarounds involve assigning list element to a variable first:
        • button0 = buttons[0]
        • @button0.clicked.connect
    • Author points out grammar is already loose enough to hack around:
      • Define function def _(x): return x
      • Then use _ as your decorator: @_(buttons[0].clicked.connect)
      • That’s less readable than just using the subscript
    • PEP proposes relaxing grammar to “any valid expression” (sort of), i.e. anything that you can use as a test in if, elif, or while blocks (as opposed to valid string input to eval)
      • Some things wouldn’t be allowed, though
      • E.g., tuples require parentheses, @f, g doesn’t make sense
      • Does a tuple as a decorator make sense in the first place, though?
    • CPython implementation on GitHub:

    Michael #2: Create a macOS Menu Bar App with Python (Pomodoro Timer)

    • by Camillo Visini
    • Nice article: Learn how to create your very own macOS Menu Bar App using Python, rumps and py2app
    • The mac menu bar is super useful. I leverage the heck out of this thing. Why not write Python for it?
    • Tools:
      • Python 3 and PyCharm as an IDE
      • Rumps → Ridiculously Uncomplicated macOS Python Statusbar apps
      • py2app → For creating standalone macOS apps from Python code (how cool is that?)
    • Get started with the code:
        app = rumps.App("Pomodoro", "🍅")
    • Then easily use Py2App to convert this into a full macOS app.
    • Would love to see somebody try to submit one of these to the mac app store.

    Brian #3: Conditional Coverage

    • Nikita Sobolev - CTO of wemake.services
    • announcement post, repo
    • suggested from @OpensourceF:
    • From README.md:
      • Conditional coverage based on any rules you define!
      • Some project have different parts that relies on different environments:
        • Python version, some code is only executed on specific versions and ignored on others
        • OS version, some code might be Windows, Mac, or Linux only
        • External packages, some code is only executed when some 3rd party package is installed
    • Traditional method:
      • combine coverage data before reporting. This works ok on CI systems or with tox for multiple Python/package version.
        • Doesn’t help much locally if wanting split is due to OS dependencies
        • Requires multiple test runs to get full coverage
    • New coverage plugin
      • allows you to maintain coverage while developing locally.
      • single test run and a reasonable coverage report
      • So cool.
    • Recommend to keep conditionals to a minimum and somewhat isolated. I wouldn’t want this all over my code base.
    • Still want real full coverage on CI.

    David #4: Pycel – A library for compiling excel spreadsheets to python code & visualizing them as a graph

    • Compile an Excel file with formulas as a Python object
    • The compiler converts formulas in the spreadsheet to executable code
    • Once compiled, you can set values for cells and inspect the output in other cells
      • This is all happening in Python now, not touching Excel anymore
    • You can visualize all of the formulas as a graph to explore how formulas depend on one another
    • The author of the package wrote it to solve a problem in civilian aerospace engineering
    • Finally, with all the formulas compiled, the package can solve for variables using an optimization process
      • In original use case this was to optimize engineering parameters to produce aircraft that could actually fly
      • Author describes how using Python he increased the cases that could be optimized from 65% to 98% and reduced calculation time from 10 minutes to around 30 seconds to 1 minute.

    Michael #5: markdown-subtemplate

    • A template engine to render Markdown with external template imports and basic variable replacements.
    • Choice between data-driven server apps (typical Flask app), CMSes that let us edit content on the web such as WordPress, and even flat file systems like Pelican.
    • This should not be a black and white decision.
    • Here's how it works:
      1. You write standard markdown files for content.
      2. Markdown files can be shared and imported into your top-level markdown.
      3. Fragments of HTML can be used when css classes and other specializations are needed, but generally HTML is avoided.
      4. A dictionary of variables and their values to replace in the merged markdown is processes.
      5. Markdown content is converted to HTML and embedded in your larger site layout (e.g. within a Jinja2 template).
      6. Markdown transforms are cached to achieve very high performance regardless of the complexity of the content.
    • Extensible logging and caching. Extensible storage coming soon.
    • PRs and contributions are welcome. More to come

    Brian #6: FlakeHell

    • wemake.services, from Conditional Coverage, also makes the wemake-python-styleguide, and recommends using FlakeHell
    • Allows you to configure flake8 and plugins more easily in pyproject.toml files.
    • Provides a ramp to start using linting tools with “legacy first”:
      • flakehell baseline > .flakehell_baseline
      • specify that file in your pyproject.toml
      • flakehell lint will run your liniting tools and only report new failures
      • you can start fixing older stuff later, or just apply style guide to new code.
    • Lots of awesome shortcuts for configuration with wildcards and such.
    • Can specify a shared config in one repo and use it multiple projects as a starting point with local changes.
    • FlakeHell:
      • It's a Flake8 wrapper to make it cool.
      • Shareable and remote configs.
      • Legacy-friendly: ability to get report only about new errors.
      • Caching for much better performance.
      • Use only specified plugins, not everything installed.
      • Manage codes per plugin.
      • Enable and disable plugins and codes by wildcard.
      • Make output beautiful.
      • pyproject.toml support.
      • Show codes for installed plugins.
      • Show all messages and codes for a plugin.
      • Check that all required plugins are installed.
      • Syntax highlighting in messages and code snippets.
      • PyLint integration.
      • Allow codes intersection for different plugins.






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