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27th Week of 2022


  • New: Beancount forecast.

    I'd like to see a forecast of the evolution of my accounts given an amount of time. Maybe by doing seasonality analysis and forecast in time series as stated here and here.

    It will also be interesting to see for a given account the evolution of the subaccounts.


  • New: Apply a style to a component given a condition.

    if you use :class you can write javascript code in the value, for example:

      class="user-retrieve-language p-2"
      :class="{'font-weight-bold': selected === language.key}"
      v-for="language in languages"
      :checked="selected === language.key"
  • New: Debug Jest tests.

    If you're not developing in Visual code, running a debugger is not easy in the middle of the tests, so to debug one you can use console.log() statements and when you run them with yarn test:unit you'll see the traces.


Type Hints

  • New: Using typing.cast.

    Sometimes the type hints of your program don't work as you expect, if you've given up on fixing the issue you can # type: ignore it, but if you know what type you want to enforce, you can use typing.cast() explicitly or implicitly from Any with type hints. With casting we can force the type checker to treat a variable as a given type.

    The main case to reach for cast() are when the type hints for a module are either missing, incomplete, or incorrect. This may be the case for third party packages, or occasionally for things in the standard library.

    Take this example:

    import datetime as dt
    from typing import cast
    from third_party import get_data
    data = get_data()
    last_import_time = cast(dt.datetime, data["last_import_time"])

    Imagine get_data() has a return type of dict[str, Any], rather than using stricter per-key types with a TypedDict. From reading the documentation or source we might find that the last_import_time key always contains a datetime object. Therefore, when we access it, we can wrap it in a cast(), to tell our type checker the real type rather than continuing with Any.

    When we encounter missing, incomplete, or incorrect type hints, we can contribute back a fix. This may be in the package itself, its related stubs package, or separate stubs in Python’s typeshed. But until such a fix is released, we will need to use cast() to make our code pass type checking.

Python Snippets

  • New: Parse an RFC2822 date.

    Interesting to test the accepted format of RSS dates.

    >>> from email.utils import parsedate_to_datetime
    >>> datestr = 'Sun, 09 Mar 1997 13:45:00 -0500'
    >>> parsedate_to_datetime(datestr)
    datetime.datetime(1997, 3, 9, 13, 45, tzinfo=datetime.timezone(datetime.timedelta(-1, 68400)))
  • New: Convert a datetime to RFC2822.

    Interesting as it's the accepted format of RSS dates.

    >>> import datetime
    >>> from email import utils
    >>> nowdt =
    >>> utils.format_datetime(nowdt)
    'Tue, 10 Feb 2020 10:06:53 -0000'
  • New: Encode url.

    import urllib.parse
    from pydantic import AnyHttpUrl
    def _normalize_url(url: str) -> AnyHttpUrl:
        """Encode url to make it compatible with AnyHttpUrl."""
        return typing.cast(
            urllib.parse.quote(url, ":/"),

    The :/ is needed when you try to parse urls that have the protocol, otherwise https://www. gets transformed into https%3A//www..


  • New: Coalescent operator.

    Is similar to the Logical OR operator (||), except instead of relying on truthy/falsy values, it relies on "nullish" values (there are only 2 nullish values, null and undefined).

    This means it's safer to use when you treat falsy values like 0 as valid.

    Similar to Logical OR, it functions as a control-flow operator; it evaluates to the first not-nullish value.

    It was introduced in Chrome 80 / Firefox 72 / Safari 13.1. It has no IE support.

    console.log(4 ?? 5);
    // 4, since neither value is nullish
    console.log(null ?? 10);
    // 10, since 'null' is nullish
    console.log(undefined ?? 0);
    // 0, since 'undefined' is nullish
    // Here's a case where it differs from
    // Logical OR (||):
    console.log(0 ?? 5); // 0
    console.log(0 || 5); // 5

Javascript snippets

Operating Systems


Linux Snippets

  • New: Git checkout to main with master as a fallback.

    I usually use the alias gcm to change to the main branch of the repository, given the change from main to master now I have some repos that use one or the other, but I still want gcm to go to the correct one. The solution is to use:

    alias gcm='git checkout "$(git symbolic-ref refs/remotes/origin/HEAD | cut -d'/' -f4)"'


Data Analysis

Recommender Systems