code: def decrypt_diff(diff_part, password_file=None):
      
      vault = VaultLib(get_vault_password(password_file))
      old_contents, new_contents = get_contents(diff_part)
      if vault.is_encrypted(old_contents):
          old_contents = vault.decrypt(old_contents)
      if vault.is_encrypted(new_contents):
          new_contents = vault.decrypt(new_contents)
      return old_contents, new_contents
docs: Diff part is a string in the format:
  
          diff --git a/group_vars/foo b/group_vars/foo
          index c09080b..0d803bb 100644
          --- a/group_vars/foo
          +++ b/group_vars/foo
          @@ -1,32 +1,33 @@
           $ANSIBLE_VAULT;1.1;AES256
          -61316662363730313230626432303662316330323064373866616436623565613033396539366263
          -383632656663356364656531653039333965
          +30393563383639396563623339383936613866326332383162306532653239636166633162323236
          +62376161626137626133
  
      Returns a tuple of decrypted old contents and decrypted new contents.