Why string-element of list could be modified but integer-element not? Python challenge question.

Question

try:
s = [“a”, “c”]
n = [0, 2]
s[1:1] = “b”
n[1:1] = 1
except:
pass
print(s[1], n[1])

Output: b 2

Why modifying string-element of list “s” worked but same thing did not work to replacing in list “n” which is integer-element?
Thanks in advance,

Answer 1

Tricky one!

`n[1:1]` selects a sub-list, so you will need to assign a list to it, not a single number!

It works for strings, because any string is also a list at the same time.

Try running this:
x = [0,2]
x[1:1] = [1]
print(x)

c =["a","b"]
c[1:1] = "oh!"
print(c)

You will see that now, integer assignment works, and in the string case, your list actually has 3 new elements because "oh!" was split!

Answer 2

Schindlabua That's great, but for the x list, it becomes [0,1,2] instead of [0,1], that means we are inserting a new element instead of modifying an existing one. And as Sercan said, to modify by x[1] = 1 way was wrong, I'm confused here : )

Answer 3

I cannot explain how, but it works this way ...

s[1] = "b"
n[1] = 1

Answer 4

Sercan Yes I understand, and I also want to hear Schindlabua's opinion about this, no worries he is a moderator, he knows better what to do for something like this : )

Answer 5

Ipang Not sure what you mean exactly! If you run the code it says "b 2", just like Sercan said in the description. The n[1:1] throws but we ignore the exception, so the quiz did everything accurately I think :)

Edit: Like, the quizzer only wants to know what the second element is, he does not care about whether we added new elements or modified existing ones.

Answer 6

Ipang thank you for your answer, i also chose same answer in challenge, but it was wrong. Afterwards i typed the code and run it, output: b 2 , i could not get it

Answer 7

Schindlabua thank you so much, it is clear now

Answer 8

Ipang Ah that's just the range selector being what it is. `x[1:1]` actually selects zero elements, so you aren't modifying any, and you're just inserting at position 1.
I agree the code is a bit hard to read, I had to run it to see what's happening.

Answer 9

Ipang i have tried x[1] = 1 instead of x[1:1] = 1 and it worked as we expected in the first place

Answer 10

Schindlabua Big Thanks for more explanation, yet one more doubt still lingers, is it possible that quiz was faulty? I mean, assigning a new value to a certain element by referring the index is how we do it, if we were modifying a single element, but the quiz says it's wrong, I wonder that : )

Answer 11

Schindlabua Well in that case I suppose you're right, since I don't know the quiz instructions, I don't even play challenges : )

But I stand by my point, if it was to modify a list element I would do list[index] = new_value, which was declared wrong in the quiz, according to Sercan. I trust your analysis on this matter nonetheless 👍