Question

class A(): pass

a = A()
b = A()

a.b = b
b.c = 1

a.b     # this is b
getattr(a, "b") # so is this

a.b.c   # this is 1   
getattr(a, "b.c") # this raises an AttributeError

It seemed very natural to me to assume the latter. I’m sure there is a good reason for this. What is it?

Answer 1

You can’t put a period in the getattr function because getattr is like accessing the dictionary lookup of the object (but is a little bit more complex than that, due to subclassing and other Python implementation details).

If you use the ‘dir’ function on a, you’ll see the dictionary keys that correspond to your object’s attributes. In this case, the string “b.c” isn’t in the set of dictionary keys.

The only way to do this with getattr is to nest calls:

getattr(getattr(a, "b"), "c")

Luckily, the standard library has a better solution!

import operator
operator.attrgetter("b.c")(a)