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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def encipher(self,string):
 """Encipher string using Autokey cipher according to initialised key. Punctuation and whitespace are removed from the input. Example:: ciphertext = Autokey('HELLO').encipher(plaintext) :param string: The string to encipher. :returns: The enciphered string. """
           
        string = self.remove_punctuation(string)
        ret = ''
        for (i,c) in enumerate(string):
            if i<len(self.key): offset = self.a2i(self.key[i])
            else: offset = self.a2i(string[i-len(self.key)])     
            ret += self.i2a(self.a2i(c)+offset)
        return ret