Sorting list by an attribute that can be None

by

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)

More Related Contents:

  1. Unpickling a python 2 object with python 3
  2. Python 2 and Python 3 dual development
  3. What is the best way to remove accents (normalize) in a Python unicode string?
  4. Access multiple elements of list knowing their index
  5. “for line in…” results in UnicodeDecodeError: ‘utf-8’ codec can’t decode byte
  6. Nested arguments not compiling
  7. Why does Python assignment not return a value?
  8. What’s the difference between “pip install” and “python -m pip install”?
  9. Two variables in Python have same id, but not lists or tuples
  10. How to write binary data to stdout in python 3?
  11. Getting only element from a single-element list in Python?
  12. How unique is Python’s id()?
  13. Difference between python3 and python3m executables
  14. Django model “doesn’t declare an explicit app_label”
  15. Python 3 replacement for deprecated compiler.ast flatten function
  16. exec() and variable scope [duplicate]
  17. warning about too many open figures
  18. What does Python optimization (-O or PYTHONOPTIMIZE) do?
  19. How to remove or hide x-axis labels from a seaborn / matplotlib plot
  20. How can I install Python’s pip3 on my Mac?
  21. Why is `print(object)` displaying “?
  22. How to install pygame? [duplicate]
  23. “TypeError: ‘type’ object is not subscriptable” in a function signature
  24. Is having a concurrent.futures.ThreadPoolExecutor call dangerous in a FastAPI endpoint?
  25. How can I use f-string with a variable, not with a string literal?
  26. Switch between python 2.7 and python 3.5 on Mac OS X
  27. Is there a way to use asyncio.Queue in multiple threads?
  28. How to get value of variable entered from user input?
  29. Add custom form fields that are not part of the model (Django)
  30. Writing to a new file if it doesn’t exist, and appending to a file if it does

Leave a Comment