Class Variable Python vs. Ruby.

test.py

class Foo():
    bar = 1  # class variable (acting like static variable)

print 'Initial value: %s  <address: %s>' % (Foo.bar, hex(id(Foo.bar)))  # Initial address
### Initial value: 1  <address: 0x7fac604109f8>

instance1 = Foo()
print 'value: %s  <address: %s>' % (instance1.bar, hex(id(instance1.bar)))  # print static var
### value: 1  <address: 0x7fac604109f8>

instance1.bar = 2  # create a copy of class var for
print 'value: %s  <address: %s>' % (instance1.bar, hex(id(instance1.bar)))
### value: 2  <address: 0x7fac604109e0>

instance2 = Foo()
print 'value: %s  <address: %s>' % (instance2.bar, hex(id(instance2.bar)))  # print static var
### value: 1  <address: 0x7fac604109f8>


class FooFoo():
    bar = [10]  # class variable type array

print 'Initial value: %s  <address: %s>' % (FooFoo.bar, hex(id(FooFoo.bar)))  # Initial address
### Initial value: [10]  <address: 0x1004667e8>

i3 = FooFoo()
print 'value: %s  <address: %s>' % (i3.bar, hex(id(i3.bar)))  # print static var
### value: [10]  <address: 0x1004667e8>

i3.bar.append(12)
print 'value: %s  <address: %s>' % (i3.bar, hex(id(i3.bar)))  # print static var
### value: [10, 12]  <address: 0x1004667e8>

i4 = FooFoo()
print 'value: %s  <address: %s>' % (i4.bar, hex(id(i4.bar)))  # print static var
### value: [10, 12]  <address: 0x1004667e8>

## Reprint i3.bar
print 'value: %s  <address: %s>' % (i3.bar, hex(id(i3.bar)))  # print static var
### value: [10, 12]  <address: 0x1004667e8>

test.rb

# Ruby First Class object:
# When a new class is created (typically using class Name ... end), an object of type Class is created and
# assigned to a global constant (Name in this case).

class Foo
  @@bar = 1  # A class variable is shared among all objects of a class, and it is also
  # accessible to the class methods that we'll describe later.

  def getBar
    @@bar
  end

  def setBar(b)
    @@bar = b
  end
end

instance1 =  Foo.new()
puts instance1.inspect
### #<Foo:0x007ff2d1895f28>
puts "value: #{instance1.getBar} address: #{instance1.getBar.object_id.to_s(16)}"
### value: 1 address: 3

instance1.setBar(23)
puts "value: #{instance1.getBar} address: #{instance1.getBar.object_id.to_s(16)}"
### value: 23 address: 2f

instance2 = Foo.new()
puts instance2.inspect
#<Foo:0x007ff2d1895d20>
puts "value: #{instance2.getBar} address: #{instance2.getBar.object_id.to_s(16)}"
### value: 23 address: 2f