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Python

Posted by Bailey Smith
Bailey Smith
1,645 Points

Timestamp challenge

I am trying to do the timestamp challenge: Create a function named timestamp_oldest that takes any number of POSIX timestamp arguments. Return the oldest one as a datetime object.

Remember, POSIX timestamps are floats and lists have a .sort() method.

I am getting the error : 'NoneType' object is not subscriptable

I tried:

import datetime

def timestamp_oldest(*args):
    args_list = list(args)
    args_list = args_list.sort()
    return datetime.datetime.fromtimestamp(args_list[0])

3 Answers

Matthew Carr
Matthew Carr
11,220 Points
Matthew Carr
Matthew Carr
11,220 Points

Lists get sorted in place. Try the following at a python prompt:

a_list = [5, 2, 1, 6]

b_list = a_list.sort()
print(b_list)

a_list.sort()
print(a_list)

Why does it happen this way? The sort() method for lists is designed to work on the list in place. According to the help in python "help(list.sort)" the sort method always returns None. The list is sorted still exists, and has been changed to a sorted version of itself.

Jing Zhang
PLUS
Jing Zhang
Courses Plus Student 6,465 Points
Jing Zhang
Jing Zhang
Courses Plus Student 6,465 Points

example for sorted:

def timestamp_oldest(*timestamps):
    return datetime.datetime.fromtimestamp(sorted(timestamps)[0])

or just use min:

def timestamp_oldest(*timestamps):
    return datetime.datetime.fromtimestamp(min(timestamps))
wantingedwards
wantingedwards
12,177 Points
wantingedwards
wantingedwards
12,177 Points

I always get confused with sort() and the build in function sorted() but from definition, sort() doesn't return a list and that's probably why the Nonetype error. If you change your code to: args_list = sorted(args_list) that should work since it return a list