Python sorting a list of classes based on static property

Question

I have some problem that I have yet to find how to solve. I have an array of classes (not instances) that I need to sort based on some static field.

class Base2:
  pass

class C1(Base2):
  order_id = 1
  
class C3(Base2):
  order_id = 3  
  
class C2(Base2):
  order_id = 2  


import operator

subclasses_list = Base2.__subclasses__()

print(subclasses_list)

for c in subclasses_list:
  print(c.order_id)

subclasses_list_sorted = subclasses_list.sort(key=lambda x: x.order_id) # operator.attrgetter("order_id")

print(subclasses_list_sorted)

The output looks like this.

[<class '__main__.C1'>, <class '__main__.C3'>, <class '__main__.C2'>]
1
3
2
None

So, the order_id is seen when iterating over the elements in the list as the print statements show.

But, my main mystery is why the sort method returns a None. It can't deal with extracting the static field?

Any ideas? Much appreciated.