CONTINUAL INTEGRATION

Problem scenario
You want to write a Python that will test if a string is a palindrome with two other requirements. One requirement is to not use a "::" (a colon pair) in the code. The second requirement is to search for a substring that is a palindrome if the full string is not a palindrome. This substring is not any substring however: it must include the leftmost character. For this requirement we will consider a one-character string to be a palindrome.

How do you create a palindrome testing function without using a double colon that tests for substrings to be palindromic if the entire string is not a palindrome?

Solution
Here is the code:

def palindrome_tester(string_to_test):
    if (len(string_to_test) == 1):
        return string_to_test
    tempa = list(string_to_test)  # Make the string a list for reversibility
    tempa.reverse()
    for x in range(0, len(tempa)):
        # Convert the tempa list to a string via the str func, map func
        # and the join method
        string_test = ''.join(map(str, tempa))
    if (string_test == string_to_test):
        return string_to_test
    else:
        # Remove the rightmost character and test resulting string
        string_to_test = string_to_test[:-1]
        # When using recursion, use the return keyword
        return palindrome_tester(string_to_test)

string_to_test = input("Enter a string: ")
result = palindrome_tester(string_to_test)
print("The longest palindrome that can be made of the characters is:")
print(result)

Problem scenario
Your Python function prints out the value of the variable immediately before it returns the variable.  When it is assigned via the "return" statement, the value is "None".  You were expecting an integer or some other value.  What is wrong?

Solution
Does your function use recursion?  If it is using recursion rather than merely calling the function and it returns "None", use the return statement.  For example, this would cause the problem:

def coolfunction(x):
    ....
    coolfunction(x)

This rewrite of the above would solve the problem of the unwanted "None" returning from your function:

def coolfunction(x):
    ....
    return coolfunction(x)