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class Validator:

def __init__(self, name=None):

self.name = name

def __set_name__(self, cls, name):

self.name = name

@classmethod

def check(cls, value):

return value

def __set__(self, instance, value):

instance.__dict__[self.name] = self.check(value)

class Typed(Validator):

expected_type = object

@classmethod

def check(cls, value):

if not isinstance(value, cls.expected_type):

raise TypeError(f'expected {cls.expected_type}')

return super().check(value)

class Integer(Typed):

expected_type = int

class Float(Typed):

expected_type = float

class String(Typed):

expected_type = str

class Positive(Validator):

@classmethod

def check(cls, value):

if value < 0:

raise ValueError('must be >= 0')

return super().check(value)

class NonEmpty(Validator):

@classmethod

def check(cls, value):

if len(value) == 0:

raise ValueError('must be non-empty')

return super().check(value)

class PositiveInteger(Integer, Positive):

pass

class PositiveFloat(Float, Positive):

pass

class NonEmptyString(String, NonEmpty):

pass

from inspect import signature

class ValidatedFunction:

def __init__(self, func):

self.func = func

self.signature = signature(func)

self.annotations = dict(func.__annotations__)

self.retcheck = self.annotations.pop('return', None)

def __call__(self, *args, **kwargs):

bound = self.signature.bind(*args, **kwargs)

for name, val in self.annotations.items():

val.check(bound.arguments[name])

result = self.func(*args, **kwargs)

if self.retcheck:

self.retcheck.check(result)

return result

# Examples

if __name__ == '__main__':

def add(x:Integer, y:Integer) -> Integer:

return x + y

add = ValidatedFunction(add)

class Stock:

name = NonEmptyString()

shares = PositiveInteger()

price = PositiveFloat()

def __init__(self, name, shares, price):

self.name = name

self.shares = shares

self.price = price

def __repr__(self):

return f'Stock({self.name!r}, {self.shares!r}, {self.price!r})'

@property

def cost(self):

return self.shares * self.price

def sell(self, nshares):

self.shares -= nshares

sell = ValidatedFunction(sell) # Broken