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Palindrome (A)

Use incremental developent to check if word is palindrome. A palindrome is a word that is spelled the same backward and forward.

First step

Make the function's definition skeleton. 
 
"""Palindrome string
Use incremental development to check if string is palindrome
A palindrome is a word that is spelled the same backward and forward.
Example: noon, redivider
We use built-in function len() to check the string length.

Version 1: define function
"""

def is_palindrome(word):
    return True

assert is_palindrome("abc") == True

Second step

Test if first is different than last. 
 
"""Palindrome string
Use incremental development to check if string is palindrome
A palindrome is a word that is spelled the same backward and forward.
Example: noon, redivider
We use built-in function len() to check the string length.

Version 2: test first/last
"""

def is_palindrome(word):
    first = word[0]
    last = word[-1]
    if (first != last):
        return False
    return True

assert is_palindrome("abca") == True
assert is_palindrome("abc") == False

Third step

Test if the middle is palindrome. 
 
"""Palindrome string
Use incremental development to check if string is palindrome
A palindrome is a word that is spelled the same backward and forward.
Example: noon, redivider

Version 3: test middle
"""

def is_palindrome(word):
    if (word[0] != word[-1]):
        return False
    if (len(word) > 2):
        middle = word[1:-1]
        return is_palindrome(middle)
    return True

assert is_palindrome("abcba") == True
assert is_palindrome("abca") == False

Final version

The final verions contains all the refactoring. 
 
"""Palindrome string
Use incremental development to check if string is palindrome
A palindrome is a word that is spelled the same backward and forward.
Example: noon, redivider

Final version: refactoring
"""

def first(word): 
    return word[0]

def last(word): 
    return word[-1]

def middle(word): 
    return word[1:-1]

def is_palindrome(word):
    if (first(word) != last(word)):
        return False
    if (len(word) > 2):   
        return is_palindrome(middle(word))
    return True

assert is_palindrome("noon") == True
assert is_palindrome("redivider") == True
assert is_palindrome("to")  == False
assert is_palindrome("moomm") == False

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