typing.TypeGuard not eliminating type possibility when branching. #3450
Description
Note: if you are reporting a wrong signature of a function or a class in the standard library, then the typeshed tracker is better suited for this report: https://github.com/python/typeshed/issues.
Describe the bug
When using TypeGuards to determine a type, they do not exhaust the type in following type checks.
Expected behavior
After a type is used in one branch, it will not show up in another.
Screenshots or Code
Current
import typing as t
def str_not_int(x: str | int) -> t.TypeGuard[str]:
return isinstance(x, str)
def f(x: str | int) -> None:
if str_not_int(x):
reveal_type(x) # Type of "x" is "str"
else:
reveal_type(x) # Type of "x" is "str | int"
def g(x: str| int) -> None:
if str_not_int(x):
reveal_type(x) # Type of "x" is "str"
return
reveal_type(x) # Type of "x" is "str | int"Expected
import typing as t
def str_not_int(x: str | int) -> t.TypeGuard[str]:
return isinstance(x, str)
def f(x: str | int) -> None:
if str_not_int(x):
reveal_type(x) # Type of "x" is "str"
else:
# if x was of type "str" it would have been caught by the first "if"
reveal_type(x) # Type of "x" is "int"
def g(x: str| int) -> None:
if str_not_int(x):
reveal_type(x) # Type of "x" is "str"
return
# if x was of type "str" the function would have returned
reveal_type(x) # Type of "x" is "int"VS Code extension or command-line
Both the cli and the VSCode extension report the same behavior.
CLI: pyright 1.1.245
Extension: v1.1.245
Additional context
I noticed that other type checkers like mypy and pylance both have this "issue", and was wondering if this is the intended behavior. If so, is there any way to get rid of more complex types when branching (such as Callable[..., int] vs Callable[..., Awaitable[int]]?