python sample: operator overload

op_overload.py

# sample: operator overload

class C1:
    def __init__(self):
        self.val_plus = 0
        self.val_minus = 0

    def __setattr__(self, attr, val):
        if attr=='val_plus':
            self.__dict__[attr] = val if val>0 else 0
        elif attr=='val_minus':
            self.__dict__[attr] = val if val<0 else 0
        else:
            raise AttributeError, 'no attribute: ' + attr

def print_values(o):
        print '%d\t%d' % (o.val_plus, o.val_minus)

### test
if __name__ == '__main__':
    o = C1()
    print_values(o)
    o.val_plus = 100
    print_values(o)
    o.val_plus = -100
    print_values(o)

    o.val_minus = 100
    print_values(o)
    o.val_minus = -100
    print_values(o)

    o.kkk = 100

### result
# >op_overload.py
# 0       0
# 100     0
# 0       0
# 0       0
# 0       -100
# Traceback (most recent call last):
#   File "d:\shishido\py\test\op_overload.py", line 33, in <module>
#     o.kkk = 100
#   File "d:\shishido\py\test\op_overload.py", line 14, in __setattr__
#     raise AttributeError, 'no attribute: ' + attr
# AttributeError: no attribute: kkk