If else fill variable if empty list

Question

I have lists that are empty and filled in the data. I am trying to the store last element of the list into a variable. If there are elements in the list, it is working fine. However, when I pass in a empty [] list, I get error like: IndexError: list index out of range. Which syntax I should be using for []?

ids = [
    'abc123',
    'ab233',
    '23231ad',
    'a23r2d23'
    ]

ids = []
# I tried these for empty
final = [ids if [] else ids[-1]] #error
# final = [ids if ids == None else ids == ids[-1]] # error
# final = [ids if ids == [] else ids == ids[-1]] # gives [[]] instead of []
print(final)

Basically, if an empty list is in ids, I need it to give []. If there are elements, then give the last element, which is working.

What do you expect to happen for an empty list?

NPE
– NPE

2018-11-01 17:36:33 +00:00
Commented Nov 1, 2018 at 17:36 — NPE
– NPE, Commented Nov 1, 2018 at 17:36
you want to check if ids

juanpa.arrivillaga
– juanpa.arrivillaga

2018-11-01 17:37:08 +00:00
Commented Nov 1, 2018 at 17:37 — juanpa.arrivillaga
– juanpa.arrivillaga, Commented Nov 1, 2018 at 17:37

NPE · Accepted Answer · 2018-11-01 17:38:03Z

2

Here is one way to do this:

final = ids[-1] if ids else None

(Replace None with the value you'd like final to take when the list is empty.)

answered Nov 1, 2018 at 17:38

NPE

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Comments

Chandella07 · Accepted Answer · 2018-11-01 17:49:57Z

1

you can check for a empty list by below expression.

data = []
if data:  #this returns False for empty list
    print("list is empty")
else:
    print("list has elements")

so what you can do is.

final = data[-1] if data else []
print(final)

answered Nov 1, 2018 at 17:49

Chandella07

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Comments

Prune · Accepted Answer · 2018-11-01 17:41:25Z

0

final = ids[-1] if len(ids) > 0 else []

This will handle the immediate problem. Please work through class materials or tutorials a little more for individual techniques. For instance, your phrase ids if [] doesnt' do what you (currently) seem to think: it does not check ids against the empty list -- all it does is to see whether that empty list is "truthy", and an empty list evaluates to False.

answered Nov 1, 2018 at 17:41

Prune

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Comments

BernardL · Accepted Answer · 2018-11-01 17:42:21Z

0

You are getting the error because you wont be able to select the last item if the list is empty and it will rightfully throw an IndexError.

Try this example

ids = [[i for i in range(10)] for x in range(3)]
ids.append([])

last_if_not_empty = [i[-1] for i in ids if i]

Here you filter out the non-empty list by if i which is the condition to select not empty lists. From there you can pick out the last elements of the lists.

answered Nov 1, 2018 at 17:42

BernardL

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Comments

Nagesh Mhapadi · Accepted Answer · 2018-11-01 17:49:55Z

0

a = list[-1] if not len(list)==0 else 0

answered Nov 1, 2018 at 17:49

Nagesh Mhapadi

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