b8acadd6a2
This makes it easier to read and edit (and review changes to) these files as source, even though it doesn't affect the rendering.
2.1 KiB
2.1 KiB
Narrowing in boolean expressions
In or expressions, the right-hand side is evaluated only if the left-hand side is falsy. So
when the right-hand side is evaluated, we know the left side has failed.
Similarly, in and expressions, the right-hand side is evaluated only if the left-hand side is
truthy. So when the right-hand side is evaluated, we know the left side has succeeded.
Narrowing in or
def bool_instance() -> bool:
return True
class A: ...
x: A | None = A() if bool_instance() else None
isinstance(x, A) or reveal_type(x) # revealed: None
x is None or reveal_type(x) # revealed: A
reveal_type(x) # revealed: A | None
Narrowing in and
def bool_instance() -> bool:
return True
class A: ...
x: A | None = A() if bool_instance() else None
isinstance(x, A) and reveal_type(x) # revealed: A
x is None and reveal_type(x) # revealed: None
reveal_type(x) # revealed: A | None
Multiple and arms
def bool_instance() -> bool:
return True
class A: ...
x: A | None = A() if bool_instance() else None
bool_instance() and isinstance(x, A) and reveal_type(x) # revealed: A
isinstance(x, A) and bool_instance() and reveal_type(x) # revealed: A
reveal_type(x) and isinstance(x, A) and bool_instance() # revealed: A | None
Multiple or arms
def bool_instance() -> bool:
return True
class A: ...
x: A | None = A() if bool_instance() else None
bool_instance() or isinstance(x, A) or reveal_type(x) # revealed: None
isinstance(x, A) or bool_instance() or reveal_type(x) # revealed: None
reveal_type(x) or isinstance(x, A) or bool_instance() # revealed: A | None
Multiple predicates
def bool_instance() -> bool:
return True
class A: ...
x: A | None | Literal[1] = A() if bool_instance() else None if bool_instance() else 1
x is None or isinstance(x, A) or reveal_type(x) # revealed: Literal[1]
Mix of and and or
def bool_instance() -> bool:
return True
class A: ...
x: A | None | Literal[1] = A() if bool_instance() else None if bool_instance() else 1
isinstance(x, A) or x is not None and reveal_type(x) # revealed: Literal[1]