Type hinting has helped me write code almost as much, if not more, than unit testing.
One thing I love is that with complete type hinting you get a lot more out of your LSP.
Typing dictionaries can be tricky and I recently learned about TypedDict to do exactly what I needed!
The Problem #
It might not be straight up obvious what the problem is, especially if you don’t utilize tools like mypy or flake8 in your development.
My handy-dandy nvim-lsp gives me a lot of feedback when I’m coding and it’s immensely helpful.
So with the LSP giving me constant feedback here’s the issue:
from typing import Dict, List, Union
my_dict: Dict[str, Union[List[str], str]] = {
"key_1": "val_1",
"key_2": ["ls_1", "ls_2"],
}
my_dict["key_2"].pop()
With the above script you’ll get an annoying warning about using pop on key_2.
The Solution #
Maybe you can stomach getting yelled at by your LSP but I like complete silence if at all possible.
TypedDict was the saving grace.
from typing import TypedDict
MyDict = TypedDict("MyDict", {"key_1": str, "key_2": List[str]})
my_typed_dict: MyDict = {
"key_1": "val_1",
"key_2": ["ls_1", "ls_2"],
}
my_typed_dict["key_2"].pop()
I was able to import TypedDict from typing, mypy_extensions, and typing_extensions
With TypedDict you define your custom type, match the first argument to TypedDict with the name of the variable (idk why), then type hint each key you expect in the dict!
It’s super easy and I think puts you into a position of being extremely explicit with your dictionary variables.
This isn’t always desired or appropriate but in most of my use cases it is.
RTFM #
There’s other implementation of TypedDict and while writing this I saw that most of the docs define a class for the type like this:
from typing import TypedDict
class MyDict(TypedDict):
key_1: str
key_2: List[str]
my_dict : MyDict = {'key_1': 'val_1', 'key_2': ["ls_1", "ls_2"]}
pep docs
mypy docs