I had the same problem and stumbled on this post, This is what I came up with to fix the issue:
Code:
def make_cities(self):
		cities = []
		for i in range(0,n):
			too_close = True
			while too_close ==True:
				x , y = random.randint(10,990),random.randint(10,490)
				too_close = False
				for city in cities:
					if city[0] in range(x-30,x+30) and city[1] in range(y-30,y+30):
...