Checking in parent class if children different arguments (different number of arguments) are negative?

Question

Let's suppose we have this parent class:

class Parent:
    def __init__(self):
        pass

And these two children:

class Child1(Parent):
    def __init__(self, 1stparam):
        pass

class Child2(Parent):
    def __init__(self, 1stparam, 2ndparam):
        pass

I would like a method for class Parent to check if the arguments passed are negative. For example:

class Parent:
    def __init__(self):
        pass   

    def check_data( allparameters ):
        if allparameters <0:
            return false

I would like to check_data for all childs by inheriting this method, for example:

mychild1 child1(-1)
mychild2 child2(1, -1)
[mychild1.check_data(), mychild2.check_data()]

This should return, of course, [False, False].

Why the hell do I always get -1 votes? I had +2 1 minute ago... — D1X, Oct 27 '16 at 12:03
@D1X An object can not remember which arguments were passed to its `__init__` method unless you stored them somewhere. — Stop harming Monica, Oct 27 '16 at 12:05
@anonymous Yeah, but that's not the solution. There is some people downvoting all my posts? — D1X, Oct 27 '16 at 12:07
You should look into super() if you want to call a parent class method using child objects — aliasav, Oct 27 '16 at 12:08

score 1 · Accepted Answer · edited May 23 '17 at 10:27

1

You need function with *args. Sample example:

def check_negative(*args):
    for item in args:
        if item < 0:
            return False
    else:
        return True

Sample run:

>>> check_negative(1)
True
>>> check_negative(-1)
False
>>> check_negative(1, 1)
True
>>> check_negative(1, -1)
False
>>> check_negative(-1, -1)
False

For more details, read: What do *args and **kwargs mean?

edited May 23 '17 at 10:27

Community

1
1

answered Oct 27 '16 at 12:00

Moinuddin Quadri

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I am trying to use this method inherited but does not work. I have defined the function as in OP, but it seems it doesn't count the arguments passed to `child1` or `child2`, as `len(args)` is always equal to 0. – D1X Oct 27 '16 at 18:33
`*args* work for functions which do not have restriction on amount of parameters passed. So you have to explicitly pass the pass the parameters. In case you do not want to do that, you have to store the list within the class as the object variable. In that case go with [*Tryph's Answer*](http://stackoverflow.com/a/40284279/2063361) – Moinuddin Quadri Oct 27 '16 at 18:43

Tryph · Answer 2 · 2016-10-27T12:19:45.760

You could do something like this:

class Parent(object):
    def __init__(self):
        self.data = []

    def check_data(self):
        return all(map(lambda arg: arg >= 0, self.data))


class Child1(Parent):
    def __init__(self, param_1):
        self.data = [param_1]


class Child2(Parent):
    def __init__(self, param_1, param_2):
        self.data = [param_1, param_2]


print(Child1(1).check_data())  # True
print(Child1(-1).check_data())  # False
print(Child2(1, 1).check_data())  # True
print(Child2(1, -1).check_data())  # False
print(Child2(-1, 1).check_data())  # False
print(Child2(-1, -1).check_data())  # False

The map function applies a function on each element of an iterable an returns the results in a iterable.
The lambda function returns False when provided with a negative number.
The all function returns True if all elements in the given list are True.

Checking in parent class if children different arguments (different number of arguments) are negative?

2 Answers2