How to use the pyclowder.extractors.download_file function in pyclowder

def process_dataset(parameters):
	global extractorName, workerScript, inputDirectory, outputDirectory

	# Find input files in dataset
	files = get_all_files(parameters)

	# Download files to input directory
	for fileExt in files:
		files[fileExt]['path'] = extractors.download_file(
			channel            = parameters['channel'],
			header             = parameters['header'],
			host               = parameters['host'],
			key                = parameters['secretKey'],
			fileid             = files[fileExt]['id'],
			# What's this argument for?
			intermediatefileid = files[fileExt]['id'],
			ext                = fileExt
		)
		# Restore temp filenames to original - script requires specific name formatting so tmp names aren't suitable
		files[fileExt]['old_path'] = files[fileExt]['path']
		files[fileExt]['path'] = os.path.join(inputDirectory, files[fileExt]['filename'])
		os.rename(files[fileExt]['old_path'], files[fileExt]['path'])
		print 'found %s file: %s' % (fileExt, files[fileExt]['path'])

	# Invoke terraref.sh