gistfile1.py

class Worker(object):

	@staticmethod
	def _irr(....):
		...

	def foo():
		with multiprocessing.Pool() as pool:
			results = {}
			results['gross_xirr'] = pool.apply_async(Worker._irr, (gross_stream, 0.115, 'xnpv'))
			
			# The above line yields:
			#_pickle.PicklingError: Can't pickle <class 'function'>: attribute lookup builtins.function failed