How can I create an object and add attributes to it?


I want to create a dynamic object (inside another object) in Python and then add attributes to it.

I tried:

obj = someobject
obj.a = object()
setattr(obj.a, 'somefield', 'somevalue')

but this didn’t work.

Any ideas?


I am setting the attributes from a for loop which loops through a list of values, e.g.

params = ['attr1', 'attr2', 'attr3']
obj = someobject
obj.a = object()

for p in params:
   obj.a.p # where p comes from for loop variable

In the above example I would get obj.a.attr1, obj.a.attr2, obj.a.attr3.

I used the setattr function because I didn’t know how to do obj.a.NAME from a for loop.

How would I set the attribute based on the value of p in the example above?

For details on why it doesn’t work, see Can't set attributes on instance of "object" class.

Asked By: John



The built-in object can be instantiated but can’t have any attributes set on it. (I wish it could, for this exact purpose.) It doesn’t have a __dict__ to hold the attributes.

I generally just do this:

class Object(object):

a = Object()
a.somefield = somevalue

When I can, I give the Object class a more meaningful name, depending on what kind of data I’m putting in it.

Some people do a different thing, where they use a sub-class of dict that allows attribute access to get at the keys. (d.key instead of d['key'])

Edit: For the addition to your question, using setattr is fine. You just can’t use setattr on object() instances.

params = ['attr1', 'attr2', 'attr3']
for p in params:
    setattr(obj.a, p, value)
Answered By: FogleBird

as docs say:

Note: object does not have a __dict__, so you can’t assign arbitrary attributes to an instance of the object class.

You could just use dummy-class instance.

Answered By: SilentGhost

There are a few ways to reach this goal.
Basically you need an object which is extendable.

obj.a = type('Test', (object,), {})  
obj.a.b = 'fun'  

obj.b = lambda:None

class Test:
obj.c = Test()
Answered By: evilpie

You could use my ancient Bunch recipe, but if you don’t want to make a “bunch class”, a very simple one already exists in Python — all functions can have arbitrary attributes (including lambda functions). So, the following works:

obj = someobject
obj.a = lambda: None
setattr(obj.a, 'somefield', 'somevalue')

Whether the loss of clarity compared to the venerable Bunch recipe is OK, is a style decision I will of course leave up to you.

Answered By: Alex Martelli

Which objects are you using? Just tried that with a sample class and it worked fine:

class MyClass:
  i = 123456
  def f(self):
    return "hello world"

b = MyClass()
b.c = MyClass()
setattr(b.c, 'test', 123)

And I got 123 as the answer.

The only situation where I see this failing is if you’re trying a setattr on a builtin object.

Update: From the comment this is a repetition of: Why can't you add attributes to object in python?

Answered By: jneves

Now you can do (not sure if it’s the same answer as evilpie):

MyObject = type('MyObject', (object,), {})
obj = MyObject()
obj.value = 42
Answered By: andreabedini
di = {}
for x in range(20):
    name = '_id%s' % x
    di[name] = type(name, (object), {})
    setattr(di[name], "attr", "value")
Answered By: lmokto

Try the code below:

$ python
>>> class Container(object):
...     pass 
>>> x = Container()
>>> x.a = 10
>>> x.b = 20
>>> x.banana = 100
>>> x.a, x.b, x.banana
(10, 20, 100)
>>> dir(x)
['__class__', '__delattr__', '__dict__', '__doc__', '__format__', 
'__getattribute__', '__hash__', '__init__', '__module__', '__new__',
'__reduce__', '__reduce_ex__', '__repr__', '__setattr__',     '__sizeof__', 
'__str__', '__subclasshook__', '__weakref__', 'a', 'b', 'banana']
Answered By: neldor

There is types.SimpleNamespace class in Python 3.3+:

obj = someobject
obj.a = SimpleNamespace()
for p in params:
    setattr(obj.a, p, value)
# obj.a.attr1

collections.namedtuple, typing.NamedTuple could be used for immutable objects. PEP 557 — Data Classes suggests a mutable alternative.

For a richer functionality, you could try attrs package. See an example usage. pydantic may be worth a look too.

Answered By: jfs

These solutions are very helpful during testing. Building on everyone else’s answers I do this in Python 2.7.9 (without staticmethod I get a TypeError (unbound method…):

In [11]: auth = type('', (), {})
In [12]: auth.func = staticmethod(lambda i: i * 2)
In [13]: auth.func(2)
Out[13]: 4
Answered By: Robpol86

Coming to this late in the day but here is my pennyworth with an object that just happens to hold some useful paths in an app but you can adapt it for anything where you want a sorta dict of information that you can access with getattr and dot notation (which is what I think this question is really about):

import os

def x_path(path_name):
    return getattr(x_path, path_name)

x_path.root = '/home/x'
for name in ['repository', 'caches', 'projects']:
    setattr(x_path, name, os.path.join(x_path.root, name))

This is cool because now:

In [1]: x_path.projects
Out[1]: '/home/x/projects'

In [2]: x_path('caches')
Out[2]: '/home/x/caches'

So this uses the function object like the above answers but uses the function to get the values (you can still use (getattr, x_path, 'repository') rather than x_path('repository') if you prefer).

Answered By: Paul Whipp

Other way i see, this way:

import maya.cmds

def getData(objets=None, attrs=None):
    di = {}
    for obj in objets:
        name = str(obj)
        for at in attrs:
    return di'L_vest_*_',type='aimConstraint')


The mock module is basically made for that.

import mock
obj = mock.Mock()
obj.a = 5
Answered By: Dunatotatos

You can also use a class object directly; it creates a namespace:

class a: pass
a.somefield1 = 'somevalue1'
setattr(a, 'somefield2', 'somevalue2')
Answered By: Ernesto

If we can determine and aggregate all the attributes and values together before creating the nested object, then we could create a new class that takes a dictionary argument on creation.

# python 2.7

class NestedObject():
    def __init__(self, initial_attrs):
        for key in initial_attrs:
            setattr(self, key, initial_attrs[key])

obj = someobject
attributes = { 'attr1': 'val1', 'attr2': 'val2', 'attr3': 'val3' }
obj.a = NestedObject(attributes)
>>> obj.a.attr1
>>> obj.a.attr2
>>> obj.a.attr3

We can also allow keyword arguments. See this post.

class NestedObject(object):
    def __init__(self, *initial_attrs, **kwargs):
        for dictionary in initial_attrs:
            for key in dictionary:
                setattr(self, key, dictionary[key])
        for key in kwargs:
            setattr(self, key, kwargs[key])

obj.a = NestedObject(attr1='val1', attr2='val2', attr3= 'val3')
Answered By: HarlemSquirrel

I think the easiest way is through the collections module.

import collections
FinanceCtaCteM = collections.namedtuple('FinanceCtaCte', 'forma_pago doc_pago get_total')
def get_total(): return 98989898
financtacteobj = FinanceCtaCteM(forma_pago='CONTADO', doc_pago='EFECTIVO',

print financtacteobj.get_total()
print financtacteobj.forma_pago
print financtacteobj.doc_pago
Answered By: Pjl

if you are looking for chain assignment, to do things such as django model template abstract attribute assigning:

from types import SimpleNamespace

def assign(target, *args, suffix):
    ls = target
    for i in range(len(args) - 1):
        a = args[i]
        ns = SimpleNamespace()
        setattr(ls, a, ns)
        ls = ns
    setattr(ls, args[-1], suffix)
    return ls

a = SimpleNamespace()
assign(a, 'a', 'b', 'c', suffix={'name': 'james'})
# {'name': 'james'}

which allows you to pass model as a target, and assign end attribute to it.

Answered By: Weilory

This works just fine:


If you want to set the attribute to some value, do this:

    exec("obj.a."+p+"=(the value here)")

For the value to be a string you will have to use these " instead of quotation marks unless you have the value stored in a variable.

Answered By: Vinsplayer
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