python class weave numberrows together -

i wrote following class weave multiple rows of number together, how print result?

class numberrow(object):  def __init__(self, row2):     self.row = row2     self.amount = len(row2)  def weave(self,other):     lijst = []     in range(self.amount):         lijst.append(self.row[i])         lijst.append(other.row[i])      self.row = lijst 

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from ipy_lib import file_input number_row import numberrow  '''program'''  bestand = file_input().splitlines() lijst1 = bestand[0].split() lijst2 = bestand[1].split() lijst3 = bestand[2].split()  row1 = numberrow(lijst1) row2 = numberrow(lijst2) row3 = numberrow(lijst3)  row1.weave(row2) number_list = row1.weave(row3)  print number_list 

i "nonetype" error. how can make sure class object becomes printable?

method weave not returning anything, need modify code this:

def weave(self,other):     lijst = []     in range(self.amount):         lijst.append(self.row[i])         lijst.append(other.row[i])      self.row = lijst     return self.row