为 python 分配不同的值 object

Question

I want to make a python class named "Foo" that has an attribute called "x" which is an int with a default value of 0. If I assign a posetive value to x it would automatically change to 10 and if I assign a negative value it would change it to -10. for example:

>>p = Foo()
>>print(p.x)
0
>>p.x = -45
>>print(p.x)
-10
>>p.x = 85
>>print(p.x)
10

Answer 1

Utilize the property decorator:

You first define _x as a class member in the constructor:

    def __init__(self):
        self._x = 0

and initialize it with 0 .

Then you define x as property:

    @property
    def x(self):
        return self._x

This means that we can get the values of _x through the name x .

Then you define setter for x with @x.setter :

    @x.setter
    def x(self, value):
        self._x = 10 if value > 0 else (-10 if value < 0 else 0)

This overrides the original logics for setting value to x , with the one that you defined.

ATTENTION: _x is still accessible, and if you change it the magic defined above won't hold (there is no private class members such as in other languages like C, C++, C#, Java, etc...). Things that start with _ conventionally means that they are of internal use.

Code:

class Foo(object):
    def __init__(self):
        self._x = 0

    @property
    def x(self):
        return self._x

    @x.setter
    def x(self, value):
        self._x = 10 if value > 0 else (-10 if value < 0 else 0)

p = Foo()
# 0
print(p.x)

p.x = -45
# -10
print(p.x)

p.x = 85
# 10
print(p.x)