Functional programming in Python: returning none instead of correct value -

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i wrote functional code in python , not understand why returns none instead of correct value code generates.

the purpose of script take line.split(',') csv , reassemble values inadvertently split '{value1,value2,value3}' 'value1,value2 ... valuen'.

def reassemble(list_name):     def inner_iter(head, tail):         if head[0][0] == '{':             new_head = [head[0] + ',' + tail[0]]             if tail[0][-1] == '}':                 return [new_head[0][1:-1]], tail[1:]             else:                 inner_iter(new_head, tail[1:])      def outer_iter(corrected_list, head, tail):         if tail == []:             print corrected_list + head             return corrected_list + head         else:             if head[0][0] == '{':                 head, tail = inner_iter(head, tail)                 outer_iter(corrected_list + head, [tail[0]], tail[1:])              else:                 outer_iter(corrected_list + head, [tail[0]], tail[1:])      return outer_iter([], [list_name[0]], list_name[1:])

below test: 

x = ['x','y', '{a', 'b}', 'c'] print reassemble(x)

and odd result:

['x', 'y', 'a,b', 'c'] #from print inside "outer_iter" none                   #from print reassemble(x)

note: want keep code functional exercise.

you forgot return in else clause, @ outer_iter.

in python, function not return specific value, returns none.

[edit]

full source:

def reassemble(list_name):     def inner_iter(head, tail):         if head[0][0] == '{':             new_head = [head[0] + ',' + tail[0]]             if tail[0][-1] == '}':                 return [new_head[0][1:-1]], tail[1:]             else:                 return inner_iter(new_head, tail[1:])                 #before change, control reached here upon return         #control might still reach here, in case 'if' condition not met         #implicitly "return none"      def outer_iter(corrected_list, head, tail):         if tail == []:             print corrected_list + head             return corrected_list + head         else:             if head[0][0] == '{':                 head, tail = inner_iter(head, tail)                 return outer_iter(corrected_list + head, [tail[0]], tail[1:])                 #before change, control reached here upon return             else:                 return outer_iter(corrected_list + head, [tail[0]], tail[1:])                 #before change, control reached here upon return         #before change, control reached here upon return         #implicitly "return none"      return outer_iter([], [list_name[0]], list_name[1:])

test:

x = ['x','y', '{a', 'b}', 'c'] print reassemble(x)

output:

['x', 'y', 'a,b', 'c'] ['x', 'y', 'a,b', 'c']

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