I'm trying to sort a list of objects using
my_list.sort(key=operator.attrgetter(attr_name))
but if any of the list items has attr = None
instead of attr = 'whatever'
,
then I get a TypeError: unorderable types: NoneType() < str()
In Py2 it wasn't a problem. How do I handle this in Py3?
The ordering comparison operators are stricter about types in Python 3, as described here:
The ordering comparison operators (<, <=, >=, >) raise a TypeError exception when the operands don’t have a meaningful natural ordering.
Python 2 sorts None
before any string (even empty string):
>>> None < None
False
>>> None < "abc"
True
>>> None < ""
True
In Python 3 any attempts at ordering NoneType
instances result in an exception:
>>> None < "abc"
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: unorderable types: NoneType() < str()
The quickest fix I can think of is to explicitly map None
instances into something orderable like ""
:
my_list_sortable = [(x or "") for x in my_list]
If you want to sort your data while keeping it intact, just give sort
a customized key
method:
def nonesorter(a):
if not a:
return ""
return a
my_list.sort(key=nonesorter)