simple encrypt with key and string for python -

Here's an example of what my code needs:

  encrypt ('7521068493 ',' 123 ') # 521'   
 returns   
 keys that change  0-9  For example  7   0 ,  5  is  1 ,  2  is  2 ,  1  is  3 , and so on.  
 The second string is the string that needs to be encrypted.  
 Here is my code:  
  def encrypt (key, string): in the range I (LAN): I print (string) in the string   
 I can not understand it   
 
 
  def encrypt (key , Msg): cypher = {x: y in z, z ('0123456789', key)} Encrypted = [] in C: msg: encrypted.append (cipher [C]) returns '' .join (encrypted)