>>> from codi import senar_senar

>>> s=senar_senar('123', 'abc')
>>> s
''
>>> s= senar_senar('12345', 'abcde')
>>> s
'2d'
>>> s= senar_senar('123456789', 'abcde')
>>> s
'234d'
>>> s= senar_senar('1##456789', 'abc&4')
>>> s
'aa4e'