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common iter query

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def iquery(conn, sql, rowfactory=tuple, batch=1, *args, **kwgs):
    """在给定的数据库连接conn上执行sql(可带有参数*args或命名参数**kwgs)
    rowfactory指定输出物为元组/字典(或字典的扩展类)
        /或使用用命名参数的函数的结果
    batch <= 0时, 直接全部输出
    batch == 1时, 逐记录输出
    batch >= 1时, 按指定的数量形成批次列表
    """
    from itertools import imap
    from contextlib import closing

    with closing(conn.cursor()) as curr:
        if curr.execute(sql, args or kwgs):
            if rowfactory == tuple:
                factory = tuple
            elif issubclass(rowfactory, dict):
                fields = [f[0].lower() for f in curr.description]
                factory = lambda x: rowfactory(zip(fields, x))
            else:
                fields = [f[0].lower() for f in curr.description]
                factory = lambda x: rowfactory(**dict(zip(fields, x)))

            if batch <= 0:
                yield imap(factory, curr.fetchall())
            elif batch == 1:
                for row in imap(factory, curr):
                    yield row
            else:
                rows = curr.fetchmany(batch)
                while rows:
                    yield map(factory, rows)
                    rows = curr.fetchmany(batch)

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