Promise in Python?

promise.py

#!/usr/bin/evn python2
import json
import logging
logging.basicConfig(level=logging.DEBUG)

class Promise(object):
	def __init__(self, function=lambda: None, prev=None):
		super(Promise, self).__init__()
		self.function = function
		self.prev = prev
		if not self.prev:
			self.result = self.function()
		else:
			# evaluate prev and store as arg
			self.result = self.function(self.prev.eval())

		class Then(object):
			def __call__(then_self, then_function):
				then_promise = Promise(function=then_function, prev=self)
				return then_promise
				
		self.then = Then()

	def eval(self):
		return self.result

def get(name):
	return json.dumps({"Hello": name})

def add_print(x):
	logging.info("x = %s", x)
	x += 1
	return x

Promise(lambda: get("noob")).then(json.loads).then(lambda response: response["Hello"]).then(logging.info)
Promise(lambda: 1).then(add_print).then(add_print).then(add_print).then(add_print)