2c57c2dc8a
## Summary
Add type narrowing for `isinstance(object, classinfo)` [1] checks:
```py
x = 1 if flag else "a"
if isinstance(x, int):
reveal_type(x) # revealed: Literal[1]
```
closes #13893
[1] https://docs.python.org/3/library/functions.html#isinstance
## Test Plan
New Markdown-based tests in `narrow/isinstance.md`.
---------
Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>
3.3 KiB
3.3 KiB
Narrowing for isinstance checks
Narrowing for isinstance(object, classinfo) expressions.
classinfo is a single type
x = 1 if flag else "a"
if isinstance(x, int):
reveal_type(x) # revealed: Literal[1]
if isinstance(x, str):
reveal_type(x) # revealed: Literal["a"]
if isinstance(x, int):
reveal_type(x) # revealed: Never
if isinstance(x, (int, object)):
reveal_type(x) # revealed: Literal[1] | Literal["a"]
classinfo is a tuple of types
Note: isinstance(x, (int, str)) should not be confused with
isinstance(x, tuple[(int, str)]). The former is equivalent to
isinstance(x, int | str):
x = 1 if flag else "a"
if isinstance(x, (int, str)):
reveal_type(x) # revealed: Literal[1] | Literal["a"]
if isinstance(x, (int, bytes)):
reveal_type(x) # revealed: Literal[1]
if isinstance(x, (bytes, str)):
reveal_type(x) # revealed: Literal["a"]
# No narrowing should occur if a larger type is also
# one of the possibilities:
if isinstance(x, (int, object)):
reveal_type(x) # revealed: Literal[1] | Literal["a"]
y = 1 if flag1 else "a" if flag2 else b"b"
if isinstance(y, (int, str)):
reveal_type(y) # revealed: Literal[1] | Literal["a"]
if isinstance(y, (int, bytes)):
reveal_type(y) # revealed: Literal[1] | Literal[b"b"]
if isinstance(y, (str, bytes)):
reveal_type(y) # revealed: Literal["a"] | Literal[b"b"]
classinfo is a nested tuple of types
x = 1 if flag else "a"
if isinstance(x, (bool, (bytes, int))):
reveal_type(x) # revealed: Literal[1]
Class types
class A: ...
class B: ...
def get_object() -> object: ...
x = get_object()
if isinstance(x, A):
reveal_type(x) # revealed: A
if isinstance(x, B):
reveal_type(x) # revealed: A & B
No narrowing for instances of builtins.type
t = type("t", (), {})
# This isn't testing what we want it to test if we infer anything more precise here:
reveal_type(t) # revealed: type
x = 1 if flag else "foo"
if isinstance(x, t):
reveal_type(x) # revealed: Literal[1] | Literal["foo"]
Do not use custom isinstance for narrowing
def isinstance(x, t):
return True
x = 1 if flag else "a"
if isinstance(x, int):
reveal_type(x) # revealed: Literal[1] | Literal["a"]
Do support narrowing if isinstance is aliased
isinstance_alias = isinstance
x = 1 if flag else "a"
if isinstance_alias(x, int):
reveal_type(x) # revealed: Literal[1]
Do support narrowing if isinstance is imported
from builtins import isinstance as imported_isinstance
x = 1 if flag else "a"
if imported_isinstance(x, int):
reveal_type(x) # revealed: Literal[1]
Do not narrow if second argument is not a type
x = 1 if flag else "a"
# TODO: this should cause us to emit a diagnostic during
# type checking
if isinstance(x, "a"):
reveal_type(x) # revealed: Literal[1] | Literal["a"]
# TODO: this should cause us to emit a diagnostic during
# type checking
if isinstance(x, "int"):
reveal_type(x) # revealed: Literal[1] | Literal["a"]
Do not narrow if there are keyword arguments
x = 1 if flag else "a"
# TODO: this should cause us to emit a diagnostic
# (`isinstance` has no `foo` parameter)
if isinstance(x, int, foo="bar"):
reveal_type(x) # revealed: Literal[1] | Literal["a"]