human
Solve the following python programming problem given the following code:
def import_green_button_xml(filename) : 
    'Import from Green Button XML.

    Parameters
    ----------
    filename : str
        Full path to Green Button XML file

    Returns
    -------
    out : eemeter.consumption.ConsumptionHistory
        Consumption history available for this project
    ' 
    with open (filename, 'r') as f : 
        tree = etree.parse (f) 
interval_blocks = tree.xpath ("//*[local-name() = 'IntervalBlock']") 
    def get_record(reading) : 
        usage_Wh = int (reading.xpath ("*[local-name() = 'value']") [0].text) 
        usage_kWh = (usage_Wh / 1000.0) 
        time_period = reading.xpath ("*[local-name() = 'timePeriod']") [0] 
        start_s = int (time_period.xpath ("*[local-name() = 'start']") [0].text) 
        start = datetime.fromtimestamp (start_s) 
        duration_s = int (time_period.xpath ("*[local-name() = 'duration']") [0].text) 
        end_s = (start_s + duration_s) 
        end = datetime.fromtimestamp (end_s) 
        return { 
            'value' : usage_kWh, 
            'start' : start, 
            'end' : end, 
} 
records = [] 
    for block in interval_blocks : 
        readings = block.xpath ("*[local-name() = 'IntervalReading']") 
        records.extend ([get_record (reading) for reading in readings]) 
fuel_type = 'electricity' 
    unit_str = 'kWh' 
    record_type = 'arbitrary' 
    consumption_data = ConsumptionData (records, fuel_type, unit_str, record_type) 
    return unit_str 

    
    

    Fix the buggy line: return unit_str
assistant
#Here is Python code to fix the buggy line: return unit_str
.

return consumption_data