How to use an attribute that has colon in ite name

Question

When an object attribute has colon in its name, how to use the attribute? The code where I came across this situation is :

instances = nova.servers.list()
for i in instances:
        print i.id, i.OS-EXT-SRV-ATTR:hypervisor_hostname

After looking at the link Find All Elements Given Namespaced Attribute and How do I escape a colon in Python format() when using kwargs? I tried using attr as

instances = nova.servers.list()
for i in instances:
        print i.id, i.(attr={"OS-EXT-SRV-ATTR":"hypervisor_hostname"})

But it gives error as Invalid syntax. How should I use the attribute OS-EXT-SRV-ATTR:hypervisor_hostname

How were you able to __set__ an attribute with such a name? – warvariuc Apr 02 '14 at 07:12 — warvariuc, Apr 02 '14 at 07:12
I am intrigued as to why you would want to do this. – ebarr Apr 02 '14 at 07:23 — ebarr, Apr 02 '14 at 07:23

score 2 · Answer 1 · answered Apr 02 '14 at 07:11

Don't use objects with attributes with such names. Use a dict.

It's possible to set and get attributes with invalid Python names:

Python 2.7.5+ (default, Sep 19 2013, 13:48:49) 

>>> class A():
...     pass
... 

>>> a = A()

>>> setattr(a, 'OS-EXT-SRV-ATTR:hypervisor_hostname', 'some_string')

>>> a.OS-EXT-SRV-ATTR:hypervisor_hostname
  File "<ipython-input-5-849986a021bc>", line 1
    a.OS-EXT-SRV-ATTR:hypervisor_hostname
                     ^
SyntaxError: invalid syntax


>>> getattr(a, 'OS-EXT-SRV-ATTR:hypervisor_hostname')
>>> 'some_string'

>>>

But don't do this, use a dict to store this info, not object's attributes.

Thanks for the answer. I used dict. – Veena Apr 02 '14 at 08:10 — Veena, Apr 02 '14 at 08:10

score 0 · Answer 2 · answered Dec 04 '18 at 16:35

With setattr(object, name, value) and read it with getattr(object, name[, default])¶

see also How do you programmatically set an attribute?

Why do you want to do this? I found myself in a situation where I needed wrap an AWS Cognito user fields within my own class rather than a dict.

        for attr in admin_get_user_dict['UserAttributes']:
            setattr(cognito_user, attr['Name'], attr['Value'])

In Cognito, custom attributes are prefixed by custom:[your_attr_name] so there you have it. And yes, you want to avoid this at any cost if you are designing your own classes.

How to use an attribute that has colon in ite name

2 Answers2