Patching classes in Python

Question

Suppose I have a Python class that I want to add an extra property to.

Is there any difference between

import path.MyClass
MyClass.foo = bar

and using something like :

import path.MyClass
setattr(MyClass, 'foo', bar)

?

If not, why do people seem to do the second rather than the first? (Eg. here http://concisionandconcinnity.blogspot.com/2008/10/chaining-monkey-patches-in-python.html )

Why not update you class's definition with the additional method? Why do all this "magical" stuff when you can simply edit the class definition? — S.Lott
– S.Lott, Commented Jun 8, 2009 at 12:28
In my particular problem when I asked this, the class came from a library that we didn't want to change; and we couldn't subclass it. Though agree in general. — interstar
– interstar, Commented Jun 9, 2009 at 9:50

Blixt · Accepted Answer · 2009-06-08 11:57:28Z

11

The statements are equivalent, but setattr might be used because it's the most dynamic choice of the two (with setattr you can use a variable for the attribute name.)

See: http://docs.python.org/library/functions.html#setattr

answered Jun 8, 2009 at 11:57

Blixt

50.3k13 gold badges128 silver badges156 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Blair Conrad Over a year ago

Agreed. In particular, this would be required the way patching was performed in the OP's referred-to blog entry - the name of the method was not known by the innards of the monkeypatch method.

interstar Over a year ago

thanks. But I updated the question because I still don't see that one is more dynamic than the other

interstar Over a year ago

ah ... no, I see what you mean ... sorry .. doh!

Collectives™ on Stack Overflow

Patching classes in Python

1 Answer 1

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related