What's the difference here ?

Question

names = ["Vishal", "Saras", "Sandeep"]

for name in names:
if len(name) > 6:
names.append(name)

print(names)

#This goes as infinite loop
#But if in for loop I use slicing [:] , then it works #properly

Answer 1

When you do for name in names[:]: you iterate over all items of a copy of the list. So the list you take the items from is a different list than the one you append new elements to and there won't be an infinite loop

Answer 2

You're not really slicing the list. list[:] is one way to copy the list so that changes that are made to the original list won't affect the copied list (and vice versa).

Try this:

l = [1, 2, 3]

a = l
b = l[:]

Here, "a" will just be another label for "l". Whatever you do to "a", affects "l" too and vice versa. Whereas b won't be affected by any changes you make to "l" (or "a"):

a.append(4)
print(l) # [1, 2, 3, 4] <<== changing a changed l

l.append(5)
print(a) # [1, 2, 3, 4, 5] <<== changing l changed a

print(b) # [1, 2, 3] <<== b is independent from both l and a because of [:]

Answer 3

Sandeep has more than 6 letters, so you append it to "names". Then you take the next item from "names", which is the name Sandeep that you just added, find out that it has more than 6 letters, append it to "names" and you're in an infinite loop

Answer 4

Yeah ! Understood 😊😊 Tysm

Answer 5

But when I use slicing [ : ], how it works properly then ?

Answer 6

You mean when we slice the list, iteration goes over new list and we don't care about original list,whatever may happen to it ? Is this what exactly happens ?