Python: dynamically add attributes to new-style class/obj

Question

Can I dynamically add attributes to instances of a new-style class (one that derives from object)?

Details:

I'm working with an instance of sqlite3.Connection. Simply extending the class isn't an option because I don't get the instance by calling a constructor; I get it by calling sqlite3.connect().

Building a wrapper doesn't save me much of the bulk for the code I'm writing.

Python 2.7.1

Edit

Right answers all. But I still am not reaching my goal; instances of sqlite3.Connection bar my attempts to set attributes in the following ways (as do instances of object itself). I always get an AttributeError:

> conn = sqlite3.connect([filepath])
> conn.a = 'foo'
Traceback (most recent call last):
  File "<pyshell#2>", line 1, in <module>
    conn.a = 'foo'
AttributeError: 'object' object has no attribute 'a'
> conn.__setattr__('a','foo')
Traceback (most recent call last):
  File "<pyshell#2>", line 1, in <module>
    conn.__setattr__('a','foo')
AttributeError: 'object' object has no attribute 'a'

Help?

Answer 1

Yes, unless the class is using __slots__ or preventing attribute writing by overriding __setattr__, or an internal Python class, or a Python class implemented natively (usually in C).

You can always try setting an attribute. Except for seriously weird __setattr__ implementations, assigning an attribute to an instance of a class of one of the types mentioned above should raise an AttributeError. In these cases, you'll have to use a wrapper, like this:

class AttrWrapper(object):
  def __init__(self, wrapped):
    self._wrapped = wrapped
  def __getattr__(self, n):
    return getattr(self._wrapped, n)
conn = AttrWrapper(sqlite3.connect(filepath))