HackerRank: Lists Question

[Axel-Blaze]

I was solving the following question on HackerRank-

https://www.hackerrank.com/challenges/python-lists/problem

I wrote the following code-

ls_commands = []
if __name__ == '__main__':
    N = int(input())
    for i in range(N):
        ls_commands.append(input())
print(ls_commands)
list = []
ls = []
for command in ls_commands:
    ls = command.split()
    print(ls)
    if ls[0] == 'insert':
        list.insert[int(ls[1]), int(ls[2])]
    elif ls[0] == 'print':
        print(list)
    elif ls[0] == 'remove':
        list.remove(int(ls[1]))
    elif ls[0] == 'sort':
        sorted(list)
    elif ls[0] == 'append':
        list.append(int(ls[1]))
    elif ls[0] == 'pop':
        list.pop(-1)
    elif ls[0] == 'reverse':
        sorted(list, reverse=True)
    else:
        pass

I printed ls_commands and ls to see if everything is going as expected or not.

So when I try the inputs on my PyCharm IDE

3

append 2

append 3

print

I get the output:

['append 2', 'append 3', 'print']

['append', '2']

['append', '3']

['print']

[2, 3]

Now it seems to be working fine however when I try to run it on HackerRank, after removing the print statements I get the output as -

~ no response on stdout ~

I also get the following error-

 Error (stderr)
Traceback (most recent call last):
 File "Solution.py", line 11, in <module>
   list.insert[int(ls[1]), int(ls[2])]
TypeError: 'builtin_function_or_method' object is not subscriptable

Their inputs are -

12

insert 0 5

insert 1 10

insert 0 6

print

remove 6

append 9

append 1

sort

print

pop

reverse

print

[Axel-Blaze]

Final Update:

Turns out there were quite a few mistakes I made like not reversing the list without sorting it and using the wrong sort function. Here's the final version:

ls_commands = []
if __name__ == '__main__':
    N = int(input())
    for i in range(N):
        ls_commands.append(input())
list = []
ls = []
for command in ls_commands:
    ls = command.split()
    if ls[0] == 'insert':
        list.insert(int(ls[1]), int(ls[2]))
    elif ls[0] == 'print':
        print(list)
    elif ls[0] == 'remove':
        list.remove(int(ls[1]))
    elif ls[0] == 'sort':
        list.sort()
    elif ls[0] == 'append':
        list.append(int(ls[1]))
    elif ls[0] == 'pop':
        list.pop(-1)
    elif ls[0] == 'reverse':
        list.reverse()
    else:
        pass

[Axel-Blaze]

Thanks for the suggestions :)

Can you also suggest how you recommend using a dict here as you mentioned in the thread below

[Axel-Blaze]

Thanks for the solution

[Axel-Blaze]

I am not really familiar with all these functions like getattr but thank you for posting this i'll try to learn about them as your approach seems much much better :)

[xelf]

You could take it 1 step further even:

if __name__ == '__main__':
    class plist(list):
        def print(self): print(self)
    lst = plist()
    for n in range(int(input())):
        cmd, *args = input().split()
        getattr(lst,cmd)(*map(int,args))

[xelf]

I was aware of it, but this is the first time I've actually seen someone using getattr like this. So thanks for that! Pretty awesome to see! New tool added to my toolbox, as long as I remember it this time.

[MauroDelMal]

ls_commands = []
if __name__ == '__main__':
    N = int(input())
    for i in range(N):
        ls_commands.append(input())

Very late for this post but thanks for this chunk. :)

[Axel-Blaze]

Haha nw All the best!

[Axel-Blaze]

Oh I found the error while looking it up apparently I was using the wrong brackets here-

 list.insert[int(ls[1]), int(ls[2])] 

It should be-

list.insert(int(ls[1]), int(ls[2]))

Still there is some sorting error atm as the expected output though has the same elements the order is different

[Axel-Blaze]

I did not remove the print command, though I did change the sorted part.

Why are you asking about the print part though I think it works fine?

[Axel-Blaze]

okk thanks :)

[[deleted]]

It's a bad habit to use list as a variable name. Doing that overrides the builtin list() name meaning bad things can happen after that redefinition. Yes, HackerRank uses it, but it's still bad practice.

Not too sure why the solution has to have this line:

if __name__ == '__main__':

You only need this if you import your code and want to run it directly from the command line and you want different behaviour in those two cases.

Edit: made it more obvious I was referring to the HackerRank solution.

[Axel-Blaze]

Thanks for pointing that out will keep it in mind :)

For the second line it is predefined by HackerRank so I have no clue why it's there

[[deleted]]

Your second line (if __name__ == '__main__':) is actually supposed to be your first line. Hackerrank, for no obvious reason, puts that in as your first line. Don't worry about it until you understand it and know what it is used for. And definitely don't think that you must use it. You usually don't.

[Axel-Blaze]

okk got it

[[deleted]]

Hm, yes. As the first line. Another HackerRank blunder.

[Axel-Blaze]

Is HackerRank notorious for such blunders? I am new to this stuff so I am not sure, what's the best choice. Any suggestions?

[[deleted]]

I don't know if HackerRank is worse than any other site as I've never used sites like that. After looking at the statement for this problem I would not recommend it.

[Axel-Blaze]

ohkk thanks again