The question doesn't seem to make musch sense. One cannot 'run' a class in Python - a class is a collection of methods and instance variables, and cannot be exectued per se.
I suppose if you are coming from a Java perspective, one could see executing the main() function as 'running' the class, but Python has no equivalent to that - unlike in Java, is is possible (necessary, in fact) to have code outside of a class and run it separately.
The other possible interpretation of your question is, 'how can you have a class method and call it without instantiating the class as an object?', in which case the answer is simple. Class methods are indicate with the @classmethod decorator, like so:
classmethod allows to call a method in the class Foo this way
normally it would be via the instance
class_instance = Foo()
bar = classmethod(bar)
# simpler via a decorator
Foo2.bar() # Foobar2
Foo3.bar() # Foobar3