polindrom in python function for list

Question

i need to write a function that returns true if a list is a polindrom and false if it is not :

is_palindrome([]): True
is_palindrome([‘s’]): True
is_palindrome([1,4,'g','g',4,1]): True
is_palindrome(['a','c','v']): False
is_polindrom[1,"g","1]: false

this is my code :

import copy
        def is_polindrom(lst):
          if len(lst)<=1:
           return True
          copy_lst = copy.copy(lst)
          reverse_copy = copy_lst.reverse()
          for i,j in reverse_copy,copy_lst:
             if reverse_copy[i].type()==copy_lst[j].type() and reverse_copy[i]==copy_lst[j]:
                return True
             else:
               return False

       is_polindrom([1,2])

when i use ["s"] instead of true is doesnt return anything and for :

is_polindrom([1,2]):
for i,j in reverse_copy,copy_lst:
TypeError: cannot unpack non-iterable NoneType object

i am not allowed to use negative or part indexes such as :

my_list[start:]
my_list[:end]
my_list[::step]
my_list[-idx]
my_list[:,idx]

thank you :)

Answer 1

Your code has 5 mistakes:

1. When you iterate through reverse_copy and copy_lst, you are doing

reverse_copy[i], copy_lst[j]

when you should just be doing

i, j

because in this case you are just iterating through each item, not through the INDEX of each item.

2. reverse() has no return value, therefore you cannot set a list to be the reverse list. You have to first create the list, then call

example_lst.reverse()

to reverse it.

3. You can't call type() like a method - it is a function, not a method. So instead of

i.type()

you must do

type(i)

4. In order to iterate through 2 lists at once, you must use the zip() function or else it doesn't work.

for i, j in zip(lst1, lst2):

5. You can't immediately return True after comparing one pair, otherwise when iterating through a list you'll just return True after just comparing the first items. Instead, you can add the result to an answer_list then return

all(answer_list)

which returns True if answer_list's items are all True. (The reason is_polindrom returned False for [1, 2] was because you weren't using the zip() function so you weren't actually iterating through the items.)

Below is the full corrected code (note that I used Python's built-in list function to create a copy of lst):

def is_polindrom(lst):
    if len(lst)<=1:
        return True
    copy_lst = list(lst)
    reverse_copy = list(lst)
    reverse_copy.reverse()
    answer_list = []
    for i,j in zip(reverse_copy,copy_lst):
        if type(i)==type(j) and i==j:
            answer_list.append(True)
        else:
            answer_list.append(False)
    return all(answer_list)
        
lst = [1, 2]
# Prints is_polindrom([1, 2]): False
print("is_polindrom([1, 2]): " + str(is_polindrom(lst))) 
print(lst) # Prints [1, 2]