Sorting a heterogeneous list of objects in Python

Question

I have some custom objects and dictionaries that I want to sort. I want to sort both the objects the dictionaries together. I want to sort the objects by an attribute and the dictionaries by a key.

object.name = 'Jack'
d = {'name':'Jill'}

sort_me =[object, d]

How do I sort this list using the object's name attribute and the dictionary's 'name' key?

Answer 1

What you are almost certainly looking for is to use the key= option for sorted(), which provides a function which returns an arbitrary sort key for each element. This function can check the type of its argument and take various actions. For instance:

import types

class obj(object):
    def __init__(self, arg):
        self.name = arg

def extract_name(obj):
    if type(obj) is types.DictType:
        return obj['name']
    else:
        return obj.__dict__['name']

d = { 'name': 'Jill'}    
print sorted([obj('Jack'), d], key=extract_name)

More information can be found on the Python wiki

RichieHindle's suggestion of using isinstance is a good one. And while I was at it I thought it might be nice to support arbitrary element names instead of hardcoding 'name':

def extract_elem_v2(elem_name):
    def key_extractor(obj):
        dct = obj if isinstance(obj, dict) else obj.__dict__
        return dct[elem_name]
    return key_extractor

Which you can use like so:

print sorted(list_of_stuff, key=extract_elem_v2('name'))

Answer 2

sort_me.sort(key=attr_or_itemgetter('name'))

Where attr_or_itemgetter():

class attr_or_itemgetter(object):
    def __init__(self, name):
        self.name = name
    def __call__(self, obj):
        try: return getattr(obj, name)
        except AttributeError:
            return obj[name]

NOTE: It intentionally doesn't check for dictionary type, therefore attr_or_itemgetter('items') applied to a dictionary will return dict.items method.