list.sort() returns None
list.sort() returns None in Python means sort() sorts in place and gives back None. Assigning its result throws the list away.
How do I fix list.sort() returns None?
To fix list.sort() returns None in Python, locate the line causing the error and check the values right before it runs. Most occurrences happen because of assigning the result of sort(). Apply a defensive check or safe fallback, make sure collections or objects exist before access, and verify return values from upstream functions.
What does list.sort() returns None mean?
Python marks methods that mutate by returning None. list.sort(), list.reverse() and list.append() all do this, and the None return is a deliberate signal that the object changed rather than a new one being produced.
Why does list.sort() returns None happen?
1. Assigning the result of sort()
The list is sorted correctly, then replaced with None.
Breaks
names = names.sort()Works
names.sort() # in place
# or
names = sorted(names) # new list2. Chaining off a mutating method
The chain continues on None, so the next call fails.
Breaks
first = names.sort()[0]Works
first = sorted(names)[0]How to find it in your own code
Remember the pair: sort/sorted, reverse/reversed. The bare verb mutates and returns None; the -ed form returns a new list. If a variable mysteriously becomes None, check whether the last thing assigned to it was a mutating method.
Try it: fix this bug
easyfirst_and_last("Mary Ann Smith") crashes: ValueError: too many values to unpack (expected 2, got 3).
def first_and_last(full_name):
first, last = full_name.split(" ")
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