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"""
Emit strings that contain the substring provided by the property
'grep-expression' (script raises an exception if the property is
missing).  We use the fourth 'conf' argument to retrieve the custom
'grep-expression' parameter.

When running this example, set --kv-separator to the empty string and
--num-reducers 0.
"""


def mapper(_, text, writer, conf):
    if text.find(conf['grep-expression']) >= 0:
        writer.emit("", text)
