def exists(*args, **kwargs):
"""Return an ``EXISTS`` clause as applied to a :class:`.Select` object.
Calling styles are of the following forms::
# use on an existing select()
s = select([table.c.col1]).where(table.c.col2==5)
s = exists(s)
# construct a select() at once
exists(['*'], **select_arguments).where(criterion)
# columns argument is optional, generates "EXISTS (SELECT *)"
# by default.
exists().where(table.c.col2==5)
"""
return Exists(*args, **kwargs)
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