How to get all subclasses?

aClass allSubclasses

class A(object):
    pass

class B(A):
    pass

class C(A):
    pass

A.__subclasses__()

[<class '__main__.B'>, <class '__main__.C'>]

#!/usr/bin/env ruby1.9

class Class
  def subclasses
    ObjectSpace.each_object(Class).select { |klass| klass < self }
  end
end

#!/usr/bin/env ruby

class Class
  def subclasses
    result = []
    ObjectSpace.each_object(Class) { |klass| result << klass if klass < self }
    result
  end
end

#!/usr/bin/env ruby

p Numeric.subclasses

function getSubclasses($parentClassName)
{
    $classes = array();
    foreach (get_declared_classes() as $className)
    {
    	if (is_subclass_of($className, $parentClassName))
    		$classes[] = $className;
    }

    return $classes;
}

var_dump(getSubClasses('myParentClass'));