4.1 KiB
Binary operations on integers
Basic Arithmetic
reveal_type(2 + 1) # revealed: Literal[3]
reveal_type(3 - 4) # revealed: Literal[-1]
reveal_type(3 * -1) # revealed: Literal[-3]
reveal_type(-3 // 3) # revealed: Literal[-1]
reveal_type(-3 / 3) # revealed: float
reveal_type(5 % 3) # revealed: Literal[2]
# error: [unsupported-operator] "Operator `+` is unsupported between objects of type `Literal[2]` and `Literal["f"]`"
reveal_type(2 + "f") # revealed: Unknown
def lhs(x: int):
reveal_type(x + 1) # revealed: int
reveal_type(x - 4) # revealed: int
reveal_type(x * -1) # revealed: int
reveal_type(x // 3) # revealed: int
reveal_type(x / 3) # revealed: int | float
reveal_type(x % 3) # revealed: int
def rhs(x: int):
reveal_type(2 + x) # revealed: int
reveal_type(3 - x) # revealed: int
reveal_type(3 * x) # revealed: int
reveal_type(-3 // x) # revealed: int
reveal_type(-3 / x) # revealed: int | float
reveal_type(5 % x) # revealed: int
def both(x: int):
reveal_type(x + x) # revealed: int
reveal_type(x - x) # revealed: int
reveal_type(x * x) # revealed: int
reveal_type(x // x) # revealed: int
reveal_type(x / x) # revealed: int | float
reveal_type(x % x) # revealed: int
Power
For power if the result fits in the int literal type it will be a Literal type. Otherwise the outcome is int.
largest_u32 = 4_294_967_295
reveal_type(2**2) # revealed: Literal[4]
reveal_type(1 ** (largest_u32 + 1)) # revealed: int
reveal_type(2**largest_u32) # revealed: int
def variable(x: int):
reveal_type(x**2) # revealed: int
# TODO: should be `Any` (overload 5 on `__pow__`), requires correct overload matching
reveal_type(2**x) # revealed: int
# TODO: should be `Any` (overload 5 on `__pow__`), requires correct overload matching
reveal_type(x**x) # revealed: int
If the second argument is <0, a float is returned at runtime. If the first argument is <0 but
the second argument is >=0, an int is still returned:
reveal_type(1**0) # revealed: Literal[1]
reveal_type(0**1) # revealed: Literal[0]
reveal_type(0**0) # revealed: Literal[1]
reveal_type((-1) ** 2) # revealed: Literal[1]
reveal_type(2 ** (-1)) # revealed: float
reveal_type((-1) ** (-1)) # revealed: float
Division by Zero
This error is really outside the current Python type system, because e.g. int.__truediv__ and
friends are not annotated to indicate that it's an error, and we don't even have a facility to
permit such an annotation. So arguably divide-by-zero should be a lint error rather than a type
checker error. But we choose to go ahead and error in the cases that are very likely to be an error:
dividing something typed as int or float by something known to be Literal[0].
This isn't definitely an error, because the object typed as int or float could be an instance
of a custom subclass which overrides division behavior to handle zero without error. But if this
unusual case occurs, the error can be avoided by explicitly typing the dividend as that safe custom
subclass; we only emit the error if the LHS type is exactly int or float, not if its a subclass.
a = 1 / 0 # error: "Cannot divide object of type `Literal[1]` by zero"
reveal_type(a) # revealed: float
b = 2 // 0 # error: "Cannot floor divide object of type `Literal[2]` by zero"
reveal_type(b) # revealed: int
c = 3 % 0 # error: "Cannot reduce object of type `Literal[3]` modulo zero"
reveal_type(c) # revealed: int
# error: "Cannot divide object of type `int` by zero"
reveal_type(int() / 0) # revealed: int | float
# error: "Cannot divide object of type `Literal[1]` by zero"
reveal_type(1 / False) # revealed: float
# error: [division-by-zero] "Cannot divide object of type `Literal[True]` by zero"
True / False
# error: [division-by-zero] "Cannot divide object of type `Literal[True]` by zero"
bool(1) / False
# error: "Cannot divide object of type `float` by zero"
reveal_type(1.0 / 0) # revealed: int | float
class MyInt(int): ...
# No error for a subclass of int
reveal_type(MyInt(3) / 0) # revealed: int | float