Inheriting from ChoiceField

[Jeffrey Eliasen]

I am writing a serializer field type that inherits from `ChoiceField`. In
looking at the code, I see the following:


def __init__(self, choices, **kwargs):
self.choices = choices
# ...
super(ChoiceField, self).__init__(**kwargs)

... and later in the same class I see:

choices = property(_get_choices, _set_choices)

I need to override the behavior of _get_choices(), but I don't believe it
ever gets called as setting self.choices in __init__() *should* replace the
property. Am I misunderstanding something in how Python works, or does this
class contain a bug?

Thanks in advance!

[Jeffrey Eliasen]

In reading closer, I believe the line in __init__() is supposed to be
`self._choices = choices`.

Post by Jeffrey Eliasen
I am writing a serializer field type that inherits from `ChoiceField`. In
self.choices = choices
# ...
super(ChoiceField, self).__init__(**kwargs)
choices = property(_get_choices, _set_choices)
I need to override the behavior of _get_choices(), but I don't believe it
ever gets called as setting self.choices in __init__() *should* replace the
property. Am I misunderstanding something in how Python works, or does this
class contain a bug?
Thanks in advance!

[Jeffrey Eliasen]

I've created PR 6023 to show the suspected fix and a test
case. https://github.com/encode/django-rest-framework/pull/6023

Post by Jeffrey Eliasen
In reading closer, I believe the line in __init__() is supposed to be
`self._choices = choices`.

Post by Jeffrey Eliasen
I am writing a serializer field type that inherits from `ChoiceField`. In
self.choices = choices
# ...
super(ChoiceField, self).__init__(**kwargs)
choices = property(_get_choices, _set_choices)
I need to override the behavior of _get_choices(), but I don't believe it
ever gets called as setting self.choices in __init__() *should* replace the
property. Am I misunderstanding something in how Python works, or does this
class contain a bug?
Thanks in advance!

[Xavier Ordoquy]

property doesn’t work the way you think it should.
... def set_a(self, value):
... self._a = value
... def get_a(self):
... return self._a
... a = property(get_a, set_a)
...

Post by Jeffrey Eliasen

d = Demo()
d.a = 1
d.a

1
... def get_a(self):
... print('GET_A')
... return self._a
...

Post by Jeffrey Eliasen

dd = SubDemo()
dd.a = 1
dd.a

1
... def get_a(self):
... print('GET_A')
... return self._a
... def set_a(self, value):
... print('SET_A')
... self._a = value
... a = property(get_a, set_a)
...

Post by Jeffrey Eliasen

dd2 = SubDemo2()
dd2.a = 5

SET_A

Post by Jeffrey Eliasen

dd2.a

GET_A
5
Regards,
Xavier,
Linovia.

Post by Jeffrey Eliasen
self.choices = choices
# ...
super(ChoiceField, self).__init__(**kwargs)
choices = property(_get_choices, _set_choices)
I need to override the behavior of _get_choices(), but I don't believe it ever gets called as setting self.choices in __init__() *should* replace the property. Am I misunderstanding something in how Python works, or does this class contain a bug?
Thanks in advance!
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[Jeffrey Eliasen]

Yeah, this was a complete brain fart on my part. I was thinking of the behavior of overwriting a function, not the behavior of a property under the same circimstance. My bad.

Post by Xavier Ordoquy
property doesn’t work the way you think it should.

class Demo: 

...     self._a = value
...     return self._a
...   a = property(get_a, set_a)
... 

d = Demo()
d.a = 1
d.a

1
...     print('GET_A')
...     return self._a
... 

dd = SubDemo()
dd.a = 1
dd.a

1
...     print('GET_A')
...     return self._a
...     print('SET_A')
...     self._a = value
...   a = property(get_a, set_a)
... 

 
dd2 = SubDemo2()
dd2.a = 5

SET_A

dd2.a

GET_A
5

 

Regards,
Xavier,
Linovia.
self.choices = choices
# ...
super(ChoiceField, self).__init__(**kwargs)
choices = property(_get_choices, _set_choices)
I need to override the behavior of _get_choices(), but I don't believe it ever gets called as setting self.choices in __init__() *should* replace the property. Am I misunderstanding something in how Python works, or does this class contain a bug?
Thanks in advance!
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