def add(self, elem, replace=False):
        """Add a requirement.

        :param elem: a string or :class:`Requirement` instance.
        :param replace: if `True`, packages in the set with the same name will
            be removed first.
        """
        if isinstance(elem, text_type):
            elem = Requirement.coerce(elem)
        if replace and elem in self:
            self.remove(elem)
        super(Requirements, self).add(elem)
def test_ccode_Indexed_without_looking_for_contraction():
    len_y = 5
    y = IndexedBase('y', shape=(len_y,))
    x = IndexedBase('x', shape=(len_y,))
    Dy = IndexedBase('Dy', shape=(len_y-1,))
    i = Idx('i', len_y-1)
    e=Eq(Dy[i], (y[i+1]-y[i])/(x[i+1]-x[i]))
    code0 = ccode(e.rhs, assign_to=e.lhs, contract=False)
    assert code0 == 'Dy[i] = (y[%s] - y[i])/(x[%s] - x[i]);' % (i + 1, i + 1)