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| from functools import partial | |
| def ContractProperty(name): | |
| return partial(Attribut, name) | |
| class Attribut(object): | |
| DEFAULT_ERROR_MESSAGE = "Error: contract not hold" | |
| def __init__(self, name, fset=None, fget=None, fdel=None, doc=None, contracts=None): | |
| self._name = name | |
| # list of predicates/contracts it should hold | |
| self._should = [] | |
| if doc is None and fget is not None and hasattr(fget, "__doc__"): | |
| doc = fget.__doc__ | |
| self.fget = fget or lambda inst, cls=None: getattr(inst, self._name) | |
| self.fset = fset or lambda inst, value: setattr(inst, self._name, value) | |
| self.fdel = fdel or lambda inst: raise AttributeError("Can't delete attribute") | |
| self.__doc__ = doc | |
| def shouldHold(self, func, err_msg = DEFAULT_ERROR_MESSAGE): | |
| if not isinstance(err_msg, Exception): | |
| err_msg = AttributeError(err_msg) | |
| self._should.append((func, err_msg)) | |
| def __get__(self, inst, cls=None): | |
| return self.fget(inst) | |
| def __set__(self, inst, value): | |
| for f, err in self._should_list: | |
| if not f(value): | |
| raise err | |
| self.fset(inst, value) | |
| def getter(self, func): | |
| self.fget = func | |
| def setter(self, func): | |
| self.fset = func | |
| class Foo(object): | |
| x = Attribut("_x") # hidden attribute name | |
| x.shouldHold(lambda x:x>0) | |
| x.shouldHold(lambda x:isinstance(x, int)) | |
| @x.setter | |
| def x(self, value): | |
| print("[!] Setter for x called !") | |
| self._x = value | |
| @ContractProperty("_y") | |
| def y(self): | |
| print("[!] Getter for y called !") | |
| f = Foo() | |
| f.x = 12 | |
| f.x = -4 | |
| f.x = 3.0 | |
| print(f.y) |
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