124 Posts Tagged ‘python’

(All tags.)

unittest’s new context methods in Python 3.11 (with backports)

A testing concerto

Python 3.11 only made one change to unittest, but it’s a good one: context manager methods. These methods can simplify setup and teardown logic in many cases, such as dynamic use of unittest.mock.


Why does Python log a DeprecationWarning saying “invalid escape sequence”?

Invalid essssscape sssssequence...

Take this code, which prints a shruggy man:


Python Type Hints - How to use Mypy’s always-true boolean check detection

Redundant-looking science apparatus

Sometimes code uses boolean checks on variables that can only be true. This is normally a sign of a mistake, either in the type hints or the implementation. Mypy has an optional check that can find such problematic boolean usage with its truthy-bool error code.


Python Type Hints - Make Mypy disallow implicit optional types

Optional? ¯_(ツ)_/¯

The original type hint proposal, PEP 484, initially allowed implicit optional types in function signatures. That is, a parameter with a default value of None would have its type automatically interpreted as optional. For example, this signature:


Python Type Hints - Old and new ways to write the same types

This is how evolution works, right?

As type hints have evolved, Python has added simpler, more succinct syntaxes. But you still need to know the older forms, since Mypy uses them when reporting types.


Python Type Hints - How to Do Exhaustiveness Checking

Well, that looks exhuasting.

Exhaustiveness checking is a very handy type checker feature. It ensures that all possible types of a variable are handled. If your code changes to add another possible type, you can guarantee that exhaustiveness-checked code paths handle the new case.


Python Type Hints - Lambdas don’t support type hints, but that’s okay

A tangle of lambdas (generated by Stable Diffusion)

Python has no syntax to add type hints to lambdas, but that doesn’t mean you can’t use them in type-checked code. In this post we’ll look at how Mypy can infer the types for lambdas, based on where they’re used.


Python Type Hints: How to Gradually Add Types for Third Party Packages

Gradually evolved cephalopods.

Hynek Schlawack recently described graduality as Python’s super power: the ability to prototype in the REPL, and gradually add linting, type checking, and other practices to refine your code into maintainable, production-ready software. You can also apply graduality within tools, activating checks one at a time and fixing the resulting errors as you go.


Use partial() With Django’s transaction.on_commit() to Avoid Late-Binding Bugs

I am rather partial to a nice plant.

Django’s transaction.on_commit() allows you to run a function after the current database transaction is committed. This is useful to ensure that actions with external services, like sending emails, don’t run until the relevant data is definitely saved.


How to Patch Requests to Have a Default Timeout

Summon forth the armies, but with a timeout of five seconds.

Python’s requests package is very popular. Even if you don’t use it directly, it’s highly likely one of your dependencies does.