from .version_constraint import VersionConstraint


class EmptyConstraint(VersionConstraint):

    def is_empty(self):
        return True

    def is_any(self):
        return False

    def allows(self, version):
        return False

    def allows_all(self, other):
        return other.is_empty()

    def allows_any(self, other):
        return False

    def intersect(self, other):
        return self

    def union(self, other):
        return other

    def difference(self, other):
        return self

    def __str__(self):
        return '<empty>'
