🔒 Dealing with string parameters when maintaining a Python package (typehinting, typechecking)

[fervent steppe]

I'm maintaining a scientific Python package which takes string parameters for some arguments. For example:

def method(...
    interp_method, # options being "cgrid_velocity", "partialslip", "freeslip"
):

I know that I can type annotate these using Literal[...] and define a type alias in a _typing.py file (e.g, InterpMethod = Literal[...]) to avoid repetition. What I want to know is:

• How could I do runtime typechecking here in a way that promotes a single source of truth? Is there a standard approach here? A lot of methods take interp_method as a parameter and I don't want to repeat myself

Any resources on type guarding in public APIs would be useful.

[sonic gull]

@fervent steppe

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[plucky crown]

There ain't really runtime typecheck unless you are doing it yourself

You can write a function and use TypeGuard to statically and runtime check them

!d typing.TypeGuard

[sonic gull]

typing.TypeGuard

typing.TypeGuard```
Special typing construct for marking user\-defined type guard functions.

`TypeGuard` can be used to annotate the return type of a user\-defined type guard function. `TypeGuard` only accepts a single type argument. At runtime, functions marked this way should return a boolean.

`TypeGuard` aims to benefit *type narrowing* – a technique used by static type checkers to determine a more precise type of an expression within a program’s code flow. Usually type narrowing is done by analyzing conditional code flow and applying the narrowing to a block of code. The conditional expression here is sometimes referred to as a “type guard”:

[plucky crown]

You write a function that promise it type narrow the type to the specific type (which static type checker would believe), and it is your duty to handle it by e.g. raising error

[sonic gull]

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