ruff/crates/ty_python_semantic/resources/mdtest/expression/boolean.md

Expressions

OR

def _(foo: str):
    reveal_type(True or False)  # revealed: Literal[True]
    reveal_type("x" or "y" or "z")  # revealed: Literal["x"]
    reveal_type("" or "y" or "z")  # revealed: Literal["y"]
    reveal_type(False or "z")  # revealed: Literal["z"]
    reveal_type(False or True)  # revealed: Literal[True]
    reveal_type(False or False)  # revealed: Literal[False]
    reveal_type(foo or False)  # revealed: (str & ~AlwaysFalsy) | Literal[False]
    reveal_type(foo or True)  # revealed: (str & ~AlwaysFalsy) | Literal[True]

AND

def _(foo: str):
    reveal_type(True and False)  # revealed: Literal[False]
    reveal_type(False and True)  # revealed: Literal[False]
    reveal_type(foo and False)  # revealed: (str & ~AlwaysTruthy) | Literal[False]
    reveal_type(foo and True)  # revealed: (str & ~AlwaysTruthy) | Literal[True]
    reveal_type("x" and "y" and "z")  # revealed: Literal["z"]
    reveal_type("x" and "y" and "")  # revealed: Literal[""]
    reveal_type("" and "y")  # revealed: Literal[""]

Simple function calls to bool

def _(flag: bool):
    if flag:
        x = True
    else:
        x = False

    reveal_type(x)  # revealed: bool

Complex

reveal_type("x" and "y" or "z")  # revealed: Literal["y"]
reveal_type("x" or "y" and "z")  # revealed: Literal["x"]
reveal_type("" and "y" or "z")  # revealed: Literal["z"]
reveal_type("" or "y" and "z")  # revealed: Literal["z"]
reveal_type("x" and "y" or "")  # revealed: Literal["y"]
reveal_type("x" or "y" and "")  # revealed: Literal["x"]

bool() function

Evaluates to builtin

a.py:

redefined_builtin_bool: type[bool] = bool

def my_bool(x) -> bool:
    return True

from a import redefined_builtin_bool, my_bool

reveal_type(redefined_builtin_bool(0))  # revealed: Literal[False]
reveal_type(my_bool(0))  # revealed: bool

Truthy values

reveal_type(bool(1))  # revealed: Literal[True]
reveal_type(bool((0,)))  # revealed: Literal[True]
reveal_type(bool("NON EMPTY"))  # revealed: Literal[True]
reveal_type(bool(True))  # revealed: Literal[True]

def foo(): ...

reveal_type(bool(foo))  # revealed: Literal[True]

Falsy values

reveal_type(bool(0))  # revealed: Literal[False]
reveal_type(bool(()))  # revealed: Literal[False]
reveal_type(bool(None))  # revealed: Literal[False]
reveal_type(bool(""))  # revealed: Literal[False]
reveal_type(bool(False))  # revealed: Literal[False]
reveal_type(bool())  # revealed: Literal[False]

Ambiguous values

reveal_type(bool([]))  # revealed: bool
reveal_type(bool({}))  # revealed: bool
reveal_type(bool(set()))  # revealed: bool

__bool__ returning NoReturn

from typing import NoReturn

class NotBoolable:
    def __bool__(self) -> NoReturn:
        raise NotImplementedError("This object can't be converted to a boolean")

# TODO: This should emit an error that `NotBoolable` can't be converted to a bool but it currently doesn't
#   because `Never` is assignable to `bool`. This probably requires dead code analysis to fix.
if NotBoolable():
    ...

Not callable __bool__

class NotBoolable:
    __bool__: None = None

# error: [unsupported-bool-conversion] "Boolean conversion is unsupported for type `NotBoolable`"
if NotBoolable():
    ...

Not-boolable union

def test(cond: bool):
    class NotBoolable:
        __bool__: int | None = None if cond else 3

    # error: [unsupported-bool-conversion] "Boolean conversion is unsupported for type `NotBoolable`"
    if NotBoolable():
        ...

Union with some variants implementing __bool__ incorrectly

def test(cond: bool):
    class NotBoolable:
        __bool__: None = None

    a = 10 if cond else NotBoolable()

    # error: [unsupported-bool-conversion] "Boolean conversion is unsupported for type `Literal[10] | NotBoolable`"
    if a:
        ...