lowpass_filter list+dict

def lowpass_filter(channels,
                   cutoff_freq=35,
                   sample_rate=175,
                   filter_order=7):
    """Filters channels with butterworth lowpass filter.

    Args:

        channels: list of ECG channels.
        cutoff_freq: cutoff freq in Hz used in filter, defaults to 35.
        sample_rate: sample rate of channel, defaults to 175.
        filter_order: filter order, defaults to 7.

    Returns: filtered list of channels."""
    is_dict = isinstance(channels, dict)

    if is_dict:
        filtered_channels = {}
    else:
        filtered_channels = []

    for channel in channels:
        curr_channel = channels[channel] if is_dict else channel
        filtered_channel = butter_lowpass_filter(curr_channel,
                                                 cutoff_freq=cutoff_freq,
                                                 sample_rate=sample_rate,
                                                 filter_order=filter_order)

        if is_dict:
            filtered_channels[channel] = filtered_channel
        else:
            filtered_channels.append(filtered_channel)

    return filtered_channels