':param \*elements:
A sequence of two tuples of the form ``(column, operator)`` where
column must be a column name or Column object and operator must
be a string containing the operator to use.
:param name:
Optional, the in-database name of this constraint.
:param deferrable:
Optional bool.  If set, emit DEFERRABLE or NOT DEFERRABLE when
issuing DDL for this constraint.
:param initially:
Optional string.  If set, emit INITIALLY <value> when issuing DDL
for this constraint.
:param using:
Optional string.  If set, emit USING <index_method> when issuing DDL
for this constraint. Defaults to \'gist\'.
:param where:
Optional string.  If set, emit WHERE <predicate> when issuing DDL
for this constraint.'

def __init__(self, *elements, **kw):

    ColumnCollectionConstraint.__init__(self, name=kw.get('name'), deferrable=kw.get('deferrable'), initially=kw.get('initially'), *[col for (col, op) in elements])
    self.operators = {}
    for (col_or_string, op) in elements:
        name = getattr(col_or_string, 'name', col_or_string)
        self.operators[name] = op
    self.using = kw.get('using', 'gist')
    where = kw.get('where')
    if where:
        self.where = expression._literal_as_text(where)
