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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.
Take this code, which prints a shruggy man:
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.
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:
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.
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 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.
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.
partial() With Django’s transaction.on_commit() to Avoid Late-Binding Bugs
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.
Python’s requests package is very popular. Even if you don’t use it directly, it’s highly likely one of your dependencies does.