Exercise 7.1

gistfile1.py

class Structure(object):
    _fields = []
    
    def __init__(self, *args, **kw):
        """ Generic constructor which initializes the object with the passed-
        in values, based on positional order and name in the **_fields**
        class variable.  Subclasses need to define **_fields** appropriately.
        """

        remaining_fields = self._fields[:]

        if len(args) > 0:
            if len(args) > len(self._fields):
                raise RuntimeError("Too many arguments; expected %d, got %d" % \
                        len(self._fields), len(args))
            for name, val in zip(self._fields, args):
                setattr(self, name, val)
            
            remaining_fields = self._fields[len(args):]

        if len(remaining_fields) > 0:
            for key, val in kw.iteritems():
                if key in remaining_fields:
                    setattr(self, key, val)
                elif key in self._fields:
                    raise RuntimeError("Duplicate values provided for field '%s'" % key)
                else:
                    raise RuntimeError("Unknown field '%s'" % key)

class Test(Structure):
    _fields = ["a", "b", "c"]
    def printself(self):
        print self.__dict__

t = Test()
print "[t]", 
t.printself()

t2 = Test(10, 20, 30)
print "[t2]",
t2.printself()