Show notes
Topics covered in this episode:
PEP 798: Unpacking in Comprehensions
Pandas 3.0.0rc0
typos
A couple testing topics
Extras
Joke
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Michael #1: PEP 798: Unpacking in Comprehensions
After careful deliberation, the Python Steering Council is pleased to accept PEP 798 – Unpacking in Comprehensions.
Examples
[*it for it in its] # list with the concatenation of iterables in 'its'
{*it for it in its} # set with the union of iterables in 'its'
{**d for d in dicts} # dict with the combination of dicts in 'dicts'
(*it for it in its) # generator of the concatenation of iterables in 'its'
Also: The Steering Council is happy to unanimously accept “PEP 810, Explicit lazy imports”
Brian #2: Pandas 3.0.0rc0
Pandas 3.0.0 will be released soon, and we’re on Release candidate 0
Here’s What’s new in Pands 3.0.0
Dedicated string data type by default
Inferred by default for string data (instead of object dtype)
The str dtype can only hold strings (or missing values), in contrast to object dtype. (setitem with non string fails)
The missing value sentinel is always NaN (np.nan) and follows the same missing value semantics as the other default dtypes.
Copy-on-Write
The result of any indexing operation (subsetting a DataFrame or Series in any way, i.e. including accessing a DataFrame column as a Series) or any method returning a new DataFrame or Series, always behaves as if it were a copy in terms of user API.
As a consequence, if you want to modify an object (DataFrame or Series), the only way to do this is to directly modify that object itself.
pd.col syntax can now be used in DataFrame.assign() and DataFrame.loc()
You can now do this: df.assign(c = pd.col('a') + pd.col('b'))
New Deprecation Policy
Plus more
-
Michael #3: typos
You’ve heard about codespell … what about typos?
VSCode extension and OpenVSX extension.
From Sky Kasko:
Like codespell, typos checks for known misspellings instead of only allowing words from a dictionary. But typos has some extra features I really appreciate, like finding spelling mistakes inside snake_case or camelCase words. For example, if you have the line:
*connecton_string = "sqlite:///my.db"*
codespell won't find the misspelling, but typos will. It gave me the output:
*error: `connecton` should be `connection`, `connector`
╭▸ ./main.py:1:1 │1 │ connecton_string = "sqlite:///my.db"
╰╴━━━━━━━━━*
But the main advantage for me is that typos has an LSP that supports editor integrations like a VS Code extension. As far as I can tell, codespell doesn't support editor integration. (Note that the popular Code Spell Checker VS Code extension is an unrelated project that uses a traditional dictionary approach.)
For more on the differences between codespell and typos, here's a comparison table I found in the typos repo: https://github.com/crate-ci/typos/blob/master/docs/comparison.md
By the way, though it's not mentioned in the installation instructions, typos is published on PyPI and can be installed with uv tool install typos, for example. That said, I don't bother installing it, I just use the VS Code extension and run it as a pre-commit hook. (By the way, I'm using prek instead of pre-commit now; thanks for the tip on episode #448!) It looks like typos also publishes a GitHub action, though I haven't used it.
Brian #4: A couple testing topics
slowlify
suggested by Brian Skinn
Simulate slow, overloaded, or resource-constrained machines to reproduce CI failures and hunt flaky tests.
Requires Linux with cgroups v2
Why your mock breaks later
Ned Badthelder
Ned’s taught us before to “Mock where the object is used, not where it’s defined.”
To be more explicit, but probably more confusing to mock-newbies, “don’t mock things that get imported, mock the object in the file it got imported to.”
See? That’s probably worse. Anyway, read Ned’s post.
If my project myproduct has user.py that uses the system builtin open() and we want to patch it:
DONT DO THIS: @patch("builtins.open")
This patches open() for the whole system
DO THIS: @patch("myproduct.user.open")
This patches open() for just the user.py file, which is what we want
Apparently this issue is common and is mucking up using coverage.py
Extras
Brian:
The Rise and Rise of FastAPI - mini documentary
“Building on Lean” chapter of LeanTDD is out
The next chapter I’m working on is “Finding Waste in TDD”
Notes to delete before end of show:
I’m not on track for an end of year completion of the first pass, so pushing goal to 1/31/26
As requested by a reader, I’m releasing both the full-so-far versions and most-recent-chapter
Michael:
My Vanishing Gradient’s episode is out
Django 6 is out
Joke: tabloid - A minimal programming language inspired by clickbait headlines