Why use setattr() and getattr() built-ins?

Question

From reading the docs, I understand exactly what getattr() and setattr() do. But it also says explicitly that getattr(x, 'foobar') is equivalent to x.foobar and setattr(x, 'foobar', 123) is equivalent to x.foobar = 123.

So why would I use them?

Answer 1

Because you can use a dynamic variable too:

somevar = 'foo' getattr(x, somevar) 

You can't do that with regular attribute access syntax.

Note that getattr() also takes an optional default value, to be returned if the attribute is missing:

>>> x = object() >>> getattr(x, 'foo') Traceback (most recent call last):   File "<stdin>", line 1, in <module> AttributeError: 'object' object has no attribute 'foo' >>> getattr(x, 'foo', 42) 42 

Using getattr() you can pull the attribute name from something else, not a literal:

for attrname in dir(x):     print('x.{} = {!r}'.format(attrname, getattr(x, attrname)) 

or you can use setattr() to set dynamic attributes:

for i, value in enumerate(dynamic_values):     setattr(i, 'attribute{}'.format(i), value) 

Answer 2

You use them if the attribute you want to access is a variable and not a literal string. They let you parameterize attribute access/setting.

There's no reason to do getattr(x, 'foobar'), but you might have a variable called attr that could be set to "foobar" or "otherAttr", and then do getattr(x, attr).