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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 cross_net(stream, env=False, debug=0, master=False):
 """ Generate picks using a simple envelope cross-correlation. Picks are made for each channel based on optimal moveout defined by maximum cross-correlation with master trace. Master trace will be the first trace in the stream if not set. Requires good inter-station coherance. :type stream: obspy.core.stream.Stream :param stream: Stream to pick :type env: bool :param env: To compute cross-correlations on the envelope or not. :type debug: int :param debug: Debug level from 0-5 :type master: obspy.core.trace.Trace :param master: Trace to use as master, if False, will use the first trace in stream. :returns: :class:`obspy.core.event.event.Event` .. rubric:: Example EQcorrscan .. warning:: This routine is not designed for accurate picking, rather it can be used for a first-pass at picks to obtain simple locations. Based on the waveform-envelope cross-correlation method. """

    event = Event()
    event.origins.append(Origin())
    event.creation_info = CreationInfo(author='EQcorrscan',
                                       creation_time=UTCDateTime())
    event.comments.append(Comment(text='cross_net'))
    samp_rate = stream[0].stats.sampling_rate
    if not env:
        if debug > 2:
            print('Using the raw data')
        st = stream.copy()
        st.resample(samp_rate)
    else:
        st = stream.copy()
        if debug > 2:
            print('Computing envelope')
        for tr in st:
            tr.resample(samp_rate)
            tr.data = envelope(tr.data)
    if not master:
        master = st[0]
    else:
        master = master
    master.data = np.nan_to_num(master.data)
    for i, tr in enumerate(st):
        tr.data = np.nan_to_num(tr.data)
        if debug > 2:
            msg = ' '.join(['Comparing', tr.stats.station, tr.stats.channel,
                            'with the master'])
            print(msg)
        shift_len = int(0.3 * len(tr))
        if debug > 2:
            print('Shift length is set to ' + str(shift_len) + ' samples')
        index, cc = xcorr(master, tr, shift_len)
        wav_id = WaveformStreamID(station_code=tr.stats.station,
                                  channel_code=tr.stats.channel,
                                  network_code=tr.stats.network)
        event.picks.append(Pick(time=tr.stats.starttime +
                                (index / tr.stats.sampling_rate),
                                waveform_id=wav_id,
                                phase_hint='S',
                                onset='emergent'))
        if debug > 2:
            print(event.picks[i])
    event.origins[0].time = min([pick.time for pick in event.picks]) - 1
    # event.origins[0].latitude = float('nan')
    # event.origins[0].longitude = float('nan')
    # Set arbitrary origin time
    del st
    return event