Variables in Python

Question

Here is a little script:

class Any(object):
 def __init__(self,x):
 self.x=x
l = [Any(2),Any(3),Any(7),Any(9),Any(10)]
print(len(l))
l2=[ind for ind in l]
l3=l
print(set(l2).difference(l3))
print(l2[1]==l[1])
print(l3[1]==l[1])
del l2[1]
print(len(l))
del l3[1]
print(len(l))

Why deleting an instance of Any in l2 doesn't change l, but deleting it in l3changes l although it seems not to have any difference between l2 and l3?

Thanks a lot!

• Jon Clements: l3 and l are just two names for the same list...
• nmclean: nedbatchelder.com/text/names.html

Answer 1

Because:

>>> l is l2
False
>>> l is l3
True

Binding the reference twice makes both names refer to the same object.

Answer 2

l2 is a different object created from l

l3 refers to the same object as l. So changing anything in l or l3 will affect that object and therefore will affect l and l3.

• Remi.b: l2 is a different object but both l and l2are lists of the same objects. Therefore, modifying l[2] modifies l2[2] but modifying l does not modify l2. Is it something like that?
• mishik: By deleting l2[1] you are not actually changing l2[1] object, you are removing second element from the list.