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			We already had support for homogeneous tuples (`tuple[int, ...]`). This PR extends this to also support mixed tuples (`tuple[str, str, *tuple[int, ...], str str]`). A mixed tuple consists of a fixed-length (possibly empty) prefix and suffix, and a variable-length portion in the middle. Every element of the variable-length portion must be of the same type. A homogeneous tuple is then just a mixed tuple with an empty prefix and suffix. The new data representation uses different Rust types for a fixed-length (aka heterogeneous) tuple. Another option would have been to use the `VariableLengthTuple` representation for all tuples, and to wrap the "variable + suffix" portion in an `Option`. I don't think that would simplify the method implementations much, though, since we would still have a 2×2 case analysis for most of them. One wrinkle is that the definition of the `tuple` class in the typeshed has a single typevar, and canonically represents a homogeneous tuple. When getting the class of a tuple instance, that means that we have to summarize our detailed mixed tuple type information into its "homogeneous supertype". (We were already doing this for heterogeneous types.) A similar thing happens when concatenating two mixed tuples: the variable-length portion and suffix of the LHS, and the prefix and variable-length portion of the RHS, all get unioned into the variable-length portion of the result. The LHS prefix and RHS suffix carry through unchanged. --------- Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>
		
			
				
	
	
	
	
		
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			3.5 KiB
		
	
	
	
	
	
	
	
Assignment with annotations
Annotation only transparent to local inference
x = 1
x: int
y = x
reveal_type(y)  # revealed: Literal[1]
Violates own annotation
x: int = "foo"  # error: [invalid-assignment] "Object of type `Literal["foo"]` is not assignable to `int`"
Violates previous annotation
x: int
x = "foo"  # error: [invalid-assignment] "Object of type `Literal["foo"]` is not assignable to `int`"
Tuple annotations are understood
[environment]
python-version = "3.12"
module.py:
from typing_extensions import Unpack
a: tuple[()] = ()
b: tuple[int] = (42,)
c: tuple[str, int] = ("42", 42)
d: tuple[tuple[str, str], tuple[int, int]] = (("foo", "foo"), (42, 42))
e: tuple[str, ...] = ()
f: tuple[str, *tuple[int, ...], bytes] = ("42", b"42")
g: tuple[str, Unpack[tuple[int, ...]], bytes] = ("42", b"42")
h: tuple[list[int], list[int]] = ([], [])
i: tuple[str | int, str | int] = (42, 42)
j: tuple[str | int] = (42,)
script.py:
from module import a, b, c, d, e, f, g, h, i, j
reveal_type(a)  # revealed: tuple[()]
reveal_type(b)  # revealed: tuple[int]
reveal_type(c)  # revealed: tuple[str, int]
reveal_type(d)  # revealed: tuple[tuple[str, str], tuple[int, int]]
reveal_type(e)  # revealed: tuple[str, ...]
reveal_type(f)  # revealed: tuple[str, *tuple[int, ...], bytes]
reveal_type(g)  # revealed: @Todo(PEP 646)
reveal_type(h)  # revealed: tuple[list[int], list[int]]
reveal_type(i)  # revealed: tuple[str | int, str | int]
reveal_type(j)  # revealed: tuple[str | int]
Incorrect tuple assignments are complained about
# error: [invalid-assignment] "Object of type `tuple[Literal[1], Literal[2]]` is not assignable to `tuple[()]`"
a: tuple[()] = (1, 2)
# error: [invalid-assignment] "Object of type `tuple[Literal["foo"]]` is not assignable to `tuple[int]`"
b: tuple[int] = ("foo",)
# error: [invalid-assignment] "Object of type `tuple[list[Unknown], Literal["foo"]]` is not assignable to `tuple[str | int, str]`"
c: tuple[str | int, str] = ([], "foo")
PEP-604 annotations are supported
def foo(v: str | int | None, w: str | str | None, x: str | str):
    reveal_type(v)  # revealed: str | int | None
    reveal_type(w)  # revealed: str | None
    reveal_type(x)  # revealed: str
PEP-604 in non-type-expression context
In Python 3.10 and later
[environment]
python-version = "3.10"
IntOrStr = int | str
Earlier versions
[environment]
python-version = "3.9"
# error: [unsupported-operator]
IntOrStr = int | str
Attribute expressions in type annotations are understood
import builtins
int = "foo"
a: builtins.int = 42
# error: [invalid-assignment] "Object of type `Literal["bar"]` is not assignable to `int`"
b: builtins.int = "bar"
c: builtins.tuple[builtins.tuple[builtins.int, builtins.int], builtins.int] = ((42, 42), 42)
# error: [invalid-assignment] "Object of type `Literal["foo"]` is not assignable to `tuple[tuple[int, int], int]`"
c: builtins.tuple[builtins.tuple[builtins.int, builtins.int], builtins.int] = "foo"
Future annotations are deferred
from __future__ import annotations
x: Foo
class Foo: ...
x = Foo()
reveal_type(x)  # revealed: Foo
Annotations in stub files are deferred
x: Foo
class Foo: ...
x = Foo()
reveal_type(x)  # revealed: Foo
Annotated assignments in stub files are inferred correctly
x: int = 1
reveal_type(x) # revealed: Literal[1]