# Palindrome

pal.py: 5 points

The goal of this part of the lab is to write a program that, given a string from the user, recursively determines whether or not it is a palindrome. A palindrome is any string that reads the same forward as backwards. “UFO tofu” and “No, sir, away! A papaya war is on!” are both examples of palindromes. (For this exercise, we ignore whitespace, punctuation and capitalization.)

Within `pal.py`, you should write a recursive function `is_pal(s)` that returns the Boolean `True` if `s` is a palindrome and `False` otherwise. We can recursively check whether `s` is a palindrome as follows: if `s` has length 0 or 1, then it is a palindrome. Otherwise, it is only a palindrome if the first character is the same as the last character, and the substring with those two characters removed is also a palindrome. If the first character is different from the last character, then you know it is not a palindrome.

You must use recursion to implement `is_pal`. As you write this function, please note the following two things are not allowed in order to get full credit:

1. You cannot loops for this implementation
2. You cannot use `recursive_reverse` from the Warmup as part of solving this function

You may assume `s` has been pre-processed, i.e. you can assume that all spaces and other non-letters have been removed, and all characters are lowercase. So the second example given above would actually have been input as “nosirawayapapayawarison”. Make sure your code is commented.

To complete `pal.py`, you should include a `main()` function which asks the user for a string `s`, calls `is_pal(s)` on that string, and then prints out whether the string is or is not a palidrome, as shown in the example output below.

#### Example Output

Some examples of running `python pal.py` are below.

``````Please enter a string: racecar

"racecar" is a palindrome
``````
``````Please enter a string: blargh

"blargh" is not is a palindrome
``````

Reminder

As usual, please commit and push your changes before moving on to the rest of the lab.