class Base:
	def __init__(self):
		self.data = []
	def add(self, x):
		self.data.append(x)
	def addtwice(self, x):
		self.add(x)
		self.add(x)
		
# Child extends Base
class Child(Base):
	def plus(self,a,b):
		return a+b
		
oChild=Child()
oChild.add("str1")
oChild.addtwice("up");
print oChild.data
print oChild.plus(2,3)
print str(type(oChild.data))
print type(oChild.data)
U:\code>python tt.py ['str1', 'up', 'up'] 5 <type 'list'> <type 'list'>