Multiple variable assignment showing unexpected value

Question

I have these 5 array initialized to empty value by using multiple assignment. I am trying to add a different value in each of those arrays. However it seems all arrays value are showing same values. How is this possible?

Code

arr1=arr2=arr3=arr4=arr5=[]

def test(arr,fruit):
arr.append(fruit)

test(arr1, "Apple")
test(arr2, "Anar")
test(arr3, "Orange")
test(arr4, "Fig")

print(arr1)
print(arr2)
print(arr3)
print(arr4)

Output

['Apple', 'Anar', 'Orange', 'Fig']
['Apple', 'Anar', 'Orange', 'Fig']
['Apple', 'Anar', 'Orange', 'Fig']
['Apple', 'Anar', 'Orange', 'Fig']

You assigned one list to five variables.

khelwood
– khelwood

2019-04-25 22:00:31 +00:00
Commented Apr 25, 2019 at 22:00 — khelwood
– khelwood, Commented Apr 25, 2019 at 22:00

Sheldore · Accepted Answer · 2019-04-25 22:09:50Z

2

An alternate approach is using list comprehension to do multiple assignment without creating reference to the same list as

arr1, arr2, arr3, arr4, arr5 = [[] for _ in range(5)]

answered Apr 25, 2019 at 22:09

Sheldore

39.2k9 gold badges63 silver badges76 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

andreihondrari · Accepted Answer · 2019-04-25 22:00:35Z

1

That's because all those variables point to the same array. Instead you want to initialize each one on separate lines:

arr1 = []
arr2 = []
arr3 = []
arr4 = []

answered Apr 25, 2019 at 22:00

andreihondrari

5,8335 gold badges33 silver badges61 bronze badges

4 Comments

vegabond Over a year ago

I understand initializing on separate line will work, but if I initialize on same line, then why won't it create a five separate arrays?

andreihondrari Over a year ago

@vegabond because it's similar to doing arr1=[] and then doing arr2=arr1, esentially passing the reference of the actual list from arr1 to arr2, resulting in both of the variables pointing to the same list/memory. That's just how Python is built.

khelwood Over a year ago

@vegabond You explicitly set all the variables to the same object. Why are you surprised that they're all referring to the same object?

andreihondrari Over a year ago

A simple test to check that they all point to the same object is by calling id(arr1) and id(arr2) and you will see that they are identical.

Collectives™ on Stack Overflow

Multiple variable assignment showing unexpected value

2 Answers 2

Comments

4 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

4 Comments

Your Answer

Sign up or log in

Post as a guest

Related