def __init__(self, constraint, rev=True, exists_main=False):
assert constraint is not None<EOL>self._rev = rev<EOL>self._loc, self._expr = self._create(constraint, exists_main)<EOL>self._constraint = constraint<EOL>
Create new clause from a constraint.

        :param constraint: The constraint
        :type constraint: Constraint
        :param rev: Whether to reverse the sense of the constraint, i.e. in order
        to select records that do not meet it.
        :type rev: bool
        :param exists_main: Put exists into main clause
        :type exists_main: bool
        :raise: AssertionError if constraint is None