class SpacecraftPart:
part_count = 0 # a CLASS variable: one copy, shared by every instance
def __init__(self, name, mass):
self.name = name # instance variables: one copy per object
self.mass = mass
SpacecraftPart.part_count += 1
p1 = SpacecraftPart("proptank", 1200.0)
p2 = SpacecraftPart("engine", 450.0)
p3 = SpacecraftPart("fairing", 900.0)
print(SpacecraftPart.part_count) # read from the class
print(p1.part_count) # readable from an instance too
print(p1.mass, p2.mass) # instance variables stayed separate