In [3]:

    

def idx2letter(idx):
    """Convert a numerical index to a char."""
    if 0 <= idx < 20:
        return chr(97 + idx)
    else:
        raise ValueError('A wrong idx value supplied.')


    

In [4]:

    

idx2letter(0)


    

    
Out[4]:





'a'

In [9]:

    

idx2letter(7)


    

    
Out[9]:





'h'

In [6]:

    

idx2letter(19)


    

    
Out[6]:





't'

In [7]:

    

idx2letter(-1)


    

    




---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-7-461b39d3f8af> in <module>()
----> 1 idx2letter(-1)

<ipython-input-3-d27bfc837d52> in idx2letter(idx)
      4         return chr(97 + idx)
      5     else:
----> 6         raise ValueError('A wrong idx value supplied.')

ValueError: A wrong idx value supplied.

In [8]:

    

idx2letter(20)


    

    




---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-8-d6456bfe4a1b> in <module>()
----> 1 idx2letter(20)

<ipython-input-3-d27bfc837d52> in idx2letter(idx)
      4         return chr(97 + idx)
      5     else:
----> 6         raise ValueError('A wrong idx value supplied.')

ValueError: A wrong idx value supplied.