CODEWITHSUNDEEP
pythonpython-typing
Jan Burgy
Jan Burgy

Reputation: 21

What type hint for heterogeneous variable length tuple in python?

I wrote some python code which constructs graphs as dict similar to standard lib's graphlib. Graph construction maintains a stack of partial graphs with "exit" vertices. Vertices are tuple[Graph, str] to mutate the node once the destination of that vertex becomes known. Instead of creating a special-purpose type, the partial graph plus vertices are smushed together into a tuple, a little like lisp forms. What type declaration can I use for these? I tried the below but "..." is only allowed as the second of two arguments

from typing import Optional

Graph = dict[str, Optional["Graph"]]  # None is a terminal
GraphAndVertices = tuple[Graph, tuple[Graph, str], ...]

Upvotes: 1

Views: 1649

Answers (2)

Jim
Jim

Reputation: 458

This is now supported in Python 3.11 using the new type hints for Variadic Generics, specifically for unpacking unbounded tuples here

The type hint now could be written as GraphAndVertices = tuple[Graph, *tuple[tuple[Graph, str], ...]]

Upvotes: 1

AKX
AKX

Reputation: 168913

As discussed in the comments, I don't think the tuple type is equipped for that sort of annotation.

I think you might have a better time rewriting things to

from typing import Optional

Graph = dict[str, Optional["Graph"]]
GraphAndVertices = tuple[Graph, tuple[tuple[Graph, str], ...]]

i.e. keeping the "tail" in another variable-length tuple of graph/str pairs.

Upvotes: 1

Related Questions