def load_installed_version(self):
        installed_packages = get_installed_pypackages()
        if self.package in installed_packages:
            self.version = "=={}".format(
                installed_packages[self.package].version)
def deserialize(self, value):
        value = decode(value)
        validators.validate_required(value, self._required)
        if not value:
            return None
        value = int(value)
        validators.validate_choice(value, self._choices)
        validators.validate_minimum(value, self._minimum)
        validators.validate_maximum(value, self._maximum)
        return value