Why is my Python object gets initialized incorrectly in an IPython notebook?

Question

I have following classes, which I used in a IPython 3.6 notebook:

class LaborResult:
    value = Value()
    quantity = 0.0 

class Value:
    absolute = 0
    relative = 0
    service = 0
    def add(self, anotherValue):
        self.absolute = self.absolute + anotherValue.absolute
        self.relative = self.relative + anotherValue.relative
        self.service = self.service + anotherValue.service
    def str(self):
        return 'Value(abs=' + str(self.absolute) + ', rel=' + str(self.relative) + ', srv=' + str(self.service) + ')'

I found out that value.relative is initialized to a wrong value (12 instead of 0) in some cases.

When I execute

x = Value()
x.str()

I get the correct result:

'Value(abs=0, rel=0, srv=0)'

When I change the code to

y = LaborResult()
y.value.str()

the result is

'Value(abs=0, rel=12, srv=0)'

I don't see where rel=12 came from.

Unfortunately, this error does not occur, if I remove all the other code (i. e. isolate only those two classes). What are possible causes of such behavior and how to fix it (make sure that y.value.relative == 0 in the second example)?

Update:

The error disappeared after I rewrote it as:

class Value:
    def __init__(self):
        self.absolute = 0.0
        self.relative = 0.0
        self.service = 0.0
    def add(self, anotherValue):
        self.absolute = self.absolute + anotherValue.absolute
        self.relative = self.relative + anotherValue.relative
        self.service = self.service + anotherValue.service
    def str(self):
        return 'Value(abs=' + str(self.absolute) + ', rel=' + str(self.relative) + ', srv=' + str(self.service) + ')'

class LaborResult:
    def __init__(self):
        self.value = Value()
        self.quantity = 0.0

Why is everything declared at the class level instead of in an `__init__` method? There's a chance that the class-level attributes are what is causing the issue — Edward Minnix, Aug 11 '18 at 14:46
`y.value.str()` does *not* produce that output. That said, I'm pretty sure I know what your problem is. — Aran-Fey, Aug 11 '18 at 14:47
Also, why do use define a method `str` instead of overriding `__str__` or `__repr__`? — Edward Minnix, Aug 11 '18 at 14:48
Let me know if the dupe is wrong and I'll reopen. But then you'll have to provide a [mcve]. — Aran-Fey, Aug 11 '18 at 14:48
@EdwardMinnix Thanks. That seems to have caused the problem (see update in my question). — Glory to Russia, Aug 11 '18 at 14:51

Why is my Python object gets initialized incorrectly in an IPython notebook?

0 Answers0