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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def atlasdb_open( path ):
 """ Open the atlas db. Return a connection. Return None if it doesn't exist """

    if not os.path.exists(path):
        log.debug("Atlas DB doesn't exist at %s" % path)
        return None

    con = sqlite3.connect( path, isolation_level=None )
    con.row_factory = atlasdb_row_factory
    return con