Python – How to sort a list of objects based on an attribute of the objects

countlistooppythonsorting

I've got a list of Python objects that I'd like to sort by an attribute of the objects themselves. The list looks like:

>>> ut
[<Tag: 128>, <Tag: 2008>, <Tag: <>, <Tag: actionscript>, <Tag: addresses>,
 <Tag: aes>, <Tag: ajax> ...]

Each object has a count:

>>> ut[1].count
1L

I need to sort the list by number of counts descending.

I've seen several methods for this, but I'm looking for best practice in Python.

Best Answer

# To sort the list in place...
ut.sort(key=lambda x: x.count, reverse=True)

# To return a new list, use the sorted() built-in function...
newlist = sorted(ut, key=lambda x: x.count, reverse=True)

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Python – How to check if a list is empty

if not a:
  print("List is empty")

Using the implicit booleanness of the empty list is quite pythonic.

Python – How to sort a list of dictionaries by a value of the dictionary

The sorted() function takes a key= parameter

newlist = sorted(list_to_be_sorted, key=lambda d: d['name'])

Alternatively, you can use operator.itemgetter instead of defining the function yourself

from operator import itemgetter
newlist = sorted(list_to_be_sorted, key=itemgetter('name'))

For completeness, add reverse=True to sort in descending order

newlist = sorted(list_to_be_sorted, key=itemgetter('name'), reverse=True)

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