Has using 'thing = liststr' instead of 'thing: list[str] = []' any downsides?
I have seen some people prefer to create a list of strings by using thing = list[str]() instead of thing: list[str] = []. I think it looks kinda weird, but maybe that's just because I have never seen that syntax before. Does that have any downsides?
It is also possible to use this for dicts: thing = dict[str, SomeClass](). Looks equally weird to me. Is that widely used? Would you use it? Would you point it out in a code review?
You'd always want to use varname: type_description = initial_value pattern. It's readable, is the same pattern you use in method params, and linters and IDEs recognize this pattern. And it makes sense for the type description be on the left side of the assignment operator, together with the variable it's describing.
The first one, has a implicit call to the constructor that need infer the type annotation of the result. BTW, the second form is a direct statement with a explicit type annotation, more recommended. When you see the AST of both statements, you can see the overload of calling the constructor and the use of AnnAssign (assign with type annotation) vs Assign:
In addition to what others have said, collection literals are also faster. list[str]() performs a function call that technically might not be the built-in list. Where [] is always an empty list and it can be created with less overhead.