How to get @property methods in asdict?

Question

I have something like:

from attr import attrs, attrib

@attrs
class Foo():
    max_count = attrib()
    @property
    def get_max_plus_one(self):
         return self.max_count + 1

Now when I do:

f = Foo(max_count=2)
f.get_max_plus_one =>3

I want to convert this to dict:

{'max_count':2, 'get_max_plus_one': 3}

When I used attr.asdict(f) I do not get the @property. I get only {'max_count':2}.

What is the cleanest way to achieve the above?

score 3 · Answer 1 · answered Aug 07 '18 at 19:26

In general, you would have to iterate over the classes attributes and check for instances of property and then call the properties __get__ method using the instance. So, something like:

In [16]: class A:
    ...:     @property
    ...:     def x(self):
    ...:         return 42
    ...:     @property
    ...:     def y(self):
    ...:         return 'foo'
    ...:

In [17]: a = A()

In [18]: vars(a)
Out[18]: {}

In [19]: a.x
Out[19]: 42

In [20]: a.y
Out[20]: 'foo'

In [21]: {n:p.__get__(a) for n, p in vars(A).items() if isinstance(p, property)}
Out[21]: {'x': 42, 'y': 'foo'}

score 3 · Answer 2 · answered Aug 08 '18 at 06:17

3

I’m afraid that isn’t supported by attrs at the moment. You may want to follow/comment on https://github.com/python-attrs/attrs/issues/353 which may give you what you want eventually.

answered Aug 08 '18 at 06:17

hynek

3,647
1
18
26

heemayl · Accepted Answer · 2018-08-07T20:16:07.307

1

For this case, you can use dir on the object, and get only the properties that do not start with __ i.e. ignore the magic methods:

In [496]: class Foo():
     ...:     def __init__(self):
     ...:         self.max_count = 2
     ...:     @property
     ...:     def get_max_plus_one(self):
     ...:          return self.max_count + 1
     ...:     

In [497]: f = Foo()

In [498]: {prop: getattr(f, prop) for prop in dir(f) if not prop.startswith('__')}
Out[498]: {'get_max_plus_one': 3, 'max_count': 2}

To handle the regular methods that do not start with __, you can add a callable test:

In [521]: class Foo():
     ...:     def __init__(self):
     ...:         self.max_count = 2
     ...:     @property
     ...:     def get_max_plus_one(self):
     ...:          return self.max_count + 1
     ...:     def spam(self):
     ...:         return 10
     ...:     

In [522]: f = Foo()

In [523]: {prop: getattr(f, prop) for prop in dir(f) if not (prop.startswith('__') or callable(getattr(Foo, prop, None)))}
Out[523]: {'get_max_plus_one': 3, 'max_count': 2}

edited Aug 07 '18 at 20:16

answered Aug 07 '18 at 19:25

heemayl

39,294
7
70
76

What about all the methods in `Foo`, and all the methods in the MRO of `Foo`? But `getattr` here was definitely more appropriate. – juanpa.arrivillaga Aug 07 '18 at 20:01
@juanpa.arrivillaga That gets tricky very quickly, i liked your generic approach but my solution is sort of specific. – heemayl Aug 07 '18 at 20:04
Well, my point was simply that if `Foo` has any methods, like `Foo.doStuff` you'll end up with a bunch of bound methods. – juanpa.arrivillaga Aug 07 '18 at 20:04
@juanpa.arrivillaga Fair enough. Edited. – heemayl Aug 07 '18 at 20:16
Both snippets produce the same result — so what's the point of adding the `callable` test? – martineau Nov 14 '20 at 17:15

score 0 · Answer 4 · answered Jan 25 '21 at 13:21

If you define:

import attr

def attr2dict(inst):
    dic = attr.asdict(inst)
    dic.update({n: p.__get__(inst) for n, p in vars(type(inst)).items() if isinstance(p, property)})
    return dic

Then you get what you were looking for:

>>> attr2dict(f)
{'max_count': 2, 'get_max_plus_one': 3}

How to get @property methods in asdict?

4 Answers4

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