test.py

def setup_constants(name, bases, dict):
    print name
    for idx, i in enumerate(dict['HEADER']):
        name = 'COLUMN_' + i.upper().replace(' ', '_')
        dict[name] = idx + 1

    return type(name, bases, dict)

class Test:
    __metaclass__ = setup_constants

    HEADER = ['Item', 'Qty', 'Unit price']

    def __init__(self):
        pass

    def t(self):
        print self.COLUMN_ITEM

class T2(Test):
    HEADER = ['Test', 'Item']

print T2.COLUMN_ITEM