Python: Directly access setter method of property when using the @property decorator

Question

I want to make use of properties in python while still being able to call the setter method of a property directly in some cases. The reason being, that I need to assign variables in lambda statements while using PySide/PyQt.

The following example includes two classes which should behave almost identical. One using property() and one @property.

class Test1:
    def __init__(self):
        self._x = 0

    def setx(self, value):
        print(f'x set to {value}')
        self._x = value

    x = property(fset=setx)


class Test2:
    def __init__(self):
        self._x = False

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

    @x.setter
    def x(self, value):
        print(f'x set to {value}')
        self._x = value


t1 = Test1()
print('Test1:')
t1.x = 1
setattr(t1, 'x', 2)
t1.setx(3)


t2 = Test2()
print('Test2:')
t2.x = 1
setattr(t2, 'x', 2)

This works pretty well. For class Test1 i can assign values to the variable using 3 different ways. 2 of them are possible to use in a lambda statement.

However, if I'm using the @property decorator I only have 2 ways left (As far as I can see at least!). And the only possible way to assign in a lambda statement is using setattr, which I'd rather avoid since it hurts readability in my opinion :(

Question

Is there a way to use the syntactic sugar of the @property decorator while still being able to use the setter directly?

_"The reason being, that I need to assign variables in lambda statements"_ That's not a good reason. 1) You can use a real function instead of a lambda. 2) There's [`setattr`](https://docs.python.org/3/library/functions.html#setattr). — Aran-Fey, Mar 28 '18 at 10:03
@Aran-Fey: 1) I don't really want to use real functions because I have dozens of those assignments and this would bloat my code tremendously. 2) A tiny bit ugly in my opinion, but true nevertheless :) — johnson, Mar 28 '18 at 10:40
@johnson. Surely getter/setter methods would *decrease* the bloat, since there would be no need for decorators. I also think they are much more effective and readable in pyqt/pyside programs, because they can be used as slots and are consistent with the style of the existing qt apis. — ekhumoro, Apr 01 '18 at 17:28

FHTMitchell · Accepted Answer · 2018-03-28T11:19:40.877

4

Edit: actually, there is a way to do it

class C:
    def __init__(self):
        self._x = 4
    @property
    def x(self):
        return self._x
    @x.setter
    def x(self, x):
        self._x = x        

c = C()

c.x == 4

C.x.fset(c, 3)

c.x == 3

But this is far less readable than setattr so I wouldn't use it.

No there isn't. But you shouldn't expect there to be.

Complaining you now only have two different ways to do something is not a good argument.

Like @Aran-Fey said, you can use a real def function or setattr like in your example. It is not wrong to use these and anyone worth their salt in python will understand what is going on.

edited Mar 28 '18 at 11:19

answered Mar 28 '18 at 10:14

FHTMitchell

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I'm not complaining, I'm rather trying to find out about every way possible before deciding which approach I like most and want to use in the future – johnson Mar 28 '18 at 10:43
fset is the only thing that worked for me. When I used setattr in a lamba it kept calling the getter. – Greg Harley Nov 24 '19 at 02:44

Python: Directly access setter method of property when using the @property decorator

Question

1 Answers1