Question

I am trying to port the answer to the question posed in How to sort alpha numeric set in python to Django. I have a list of Django model instances returned by a query and I can’t work out how to use lambda to construct an elegant (or otherwise!) sort function.

If my model contains a ‘name’ attribute – e.g.

result = Take.objects.all()
for i in result:
   print i.name

How can I sort the resulting list of objects by the name attribute and apply a number of tests?

i.e. my name value could be ‘1A’,’1′,’A1′,’001A’ etc

e.g.
to give this ordering (based on name)

1A
2A
10A
A1
A2
A10
A11
B2
B4

Answer 1

Use operator.attrgetter to sort your objects by the value of an attribute:

import operator

class Foo:
    def __init__(self, name):
        self.name = name

l = [Foo('AA'), Foo('a'), Foo('AB')]
l.sort(key=operator.attrgetter('name'))
print [o.name for o in l]
['AA', 'AB', 'a']

Here is another answer I provided which defines a function to perform alpha-numeric sort in “human” order. Merging the _human_key function into the example above, you could do:

l.sort(key=lambda x: _human_key(x.name))
print [o.name for o in l]
['a', 'AA', 'AB']