[Tutor] (no subject)

[Nidian Job-Smith]

Hi all,
I'm new to programming (thus Python), so after reading the basics, I wanted to practise what I've learnt . I've come across a beginners exercise which is to programme rot13.
I've written some code but it doesn't seem to work....
Here it is: 

def rot13(s):    char_low = ()    result = ""    if not s.isalpha():        return char    char_low = char_low.lower()    if char_low <= 'm':                dist = 13    else:                dist = -13    char = chr(ord(char) + dist)             def rot13_char(ch):  return ''.join( rot13(s) for char in ch )  
Any idea where i'm wrong? 
 		 	   		  
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