Question

def make_converter(match, replacement):        
    d={match : replacement}         
    return d

def apply_converter(converter, string):    
    c1= "".join(str(x) for x in converter.keys())
    c2= "".join(str(x) for x in converter.values())
    print c1,c2
    c3=string.find(c1)
    if c3==-1:
        return string
    string=string.replace(c1,c2,1)
    apply_converter(converter,string)

# For example,

c1 = make_converter('aa', 'a')
print apply_converter(c1, 'aaaa')
#>>> a

c = make_converter('aba', 'b')
print apply_converter(c, 'aaaaaabaaaaa')
#>>> ab

Answer 1

You’re not returning the result of the recursion. Your function returns the input string if no match is found, otherwise it returns nothing at all!

You want:

return apply_converter(converter, string)