Set
These types are subclasses of built-in set
type with some constraints on it.
InitHook
Type with special __init_hook__
method which is called on instantiation. It is not intended to be used without other hooks, because it does not guarantee that the set
won't be modified later in the program.
from valtypes.type.set import InitHook
from valtypes.error.parsing import Base as ParsingError
class EvenNumbers(InitHook[int]):
def __init_hook__(self) -> None:
if any(n % 2 for n in self):
raise ParsingError(f"{self.__class__.__name__} can't contain odd numbers")
EvenNumbers({2, 4, 6}) # passes
EvenNumbers({2, 3, 6}) # raises ParsingError
Warning
The code above does not keep the set
from being modified after instantiation. It can still contain odd numbers. If you want to prevent that, you can use immutable types like frozenset
instead.
LengthHook
Type with special __length_hook__
method which is called whenever the length of a set
is going to change. Calling methods like add
or update
as well as assignment operators will trigger this hook with the new length that the set
would have after the operation.
If the hook raises an exception, the operation is aborted and the set
is left unchanged.
from valtypes.type.set import LengthHook
from valtypes.error.parsing import Base as ParsingError
class WithEvenLength(LengthHook[int]):
def __length_hook__(self, new_length: int) -> None:
if new_length % 2:
raise ParsingError(f"{self.__class__.__name__} can't have odd length")
l = WithEvenLength({1, 2})
l.update({3, 4}) # passes
l.discard(5) # nothing to discard, so it passes
try:
l.pop() # raises ParsingError
# because the set would have odd length after this operation
except ParsingError:
# thus, the set is not modified
print(l) # {1, 2, 3, 4}
MinimumLength
Type for representing a set
that has a given minimum length. The minimum allowed length is stored in the __minimum_length__
attribute.
from typing import TypeVar
from valtypes.type.set import MinimumLength
T = TypeVar("T")
class AtLeastTwoElements(MinimumLength[T]):
__minimum_length__ = 2
s = AtLeastTwoElements({1, 2}) # passes
s &= {2, 3} # raises valtypes.error.parsing.type.sized.MinimumLength
MaximumLength
Type for representing a set
that has a given maximum length. The maximum allowed length is stored in the __maximum_length__
attribute.
from typing import TypeVar
from valtypes.type.set import MaximumLength
T = TypeVar("T")
class AtMostTwoElements(MaximumLength[T]):
__maximum_length__ = 2
s = AtMostTwoElements({1, 2}) # passes
s |= {2, 3} # raises valtypes.error.parsing.type.sized.MaximumLength
NonEmpty
Type for representing a non-empty set
. It is a subclass of MinimumLength
with __minimum_length__
set to 1
.
from valtypes.type.set import NonEmpty
s = NonEmpty({1}) # passes
s.clear() # raises valtypes.error.parsing.type.sized.MinimumLength