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>"