Convert from list to dictionary

carbongraph = {'(0, 1)': [(0, 2)], '(0, 2)': [(0, 1), (0, 3), (1, 2)], '(0, 3)': [(0, 2)], '(1, 2)': [(0, 2), (2, 2)], '(2, 2)': [(1, 2)]}

TypeError: object of type 'NoneType' has no len()

 carbongraph = {'(0, 1)':['(0, 2)'], '(0, 2)':['(0, 1)','(0, 3)','(1, 2)'],
'(0, 3)':['(0, 2)'], '(1, 2)' :['(0, 2)','(2, 2)'], '(2, 2)':['(1, 2)']}

grid = [[0,1,1,1],
        [0,0,1,0],
        [0,0,1,0]]
        
lst = []
for rows, row in enumerate(grid) :
    for cols, col in enumerate(row) :
        if grid[rows][cols] in [1] :
            lst.append((rows, cols))
            
       
print (lst)
        

adjacencylist = []

def adjacentnode(nodea,nodeb):
    if nodea[0] == nodeb[0] and nodea[1] == nodeb[1] + 1:
        adjacent = True
    elif nodea[0] == nodeb[0] and nodea[1] == nodeb[1]-1:
        adjacent = True
    elif nodea[1] == nodeb[1] and nodea[0] == nodeb[0]+1:
        adjacent = True
    elif nodea[1] == nodeb[1] and nodea[0] == nodeb[0]-1:
        adjacent = True
    else:
        adjacent = False
    return adjacent

#Below is where conversion happens
carbongraph = {}
for node in range(len(lst)):
    adjacencylist.append((lst[node],[]))
    for neighbour in range(len(lst)):
        adjacentnodes = (adjacentnode(lst[node],lst[neighbour]))
        
        if adjacentnodes == True:
            adjacencylist[node][1].append(lst[neighbour])
        
for item in adjacencylist:
    carbongraph[str(item[0])] = (item[(1)])
    for adj in item[1]:
        adj = str(adj)
    
def shortestpath(graph, start, end, path = []):
  path = path + [start]
  if start == end:
      return path
  if start not in graph:
      return None
  for node in graph[start]:
      if node not in path:
          newpath = shortestpath(graph, node, end, path)
          if newpath: 
            return newpath
  return None

LeafArray = []
for leaf in carbongraph:
  degree = (len(carbongraph[leaf]))
  if degree == 1:
    
    LeafArray.append(leaf)
print(LeafArray)

chainlist = []
for node in LeafArray:
    for neighbour in LeafArray:
      currentpath = (shortestpath(carbongraph,node,neighbour))
      carbonchain = len(currentpath)#error occurs here
      print (currentpath)
      chainlist.append(carbonchain)
      
longestchain = max(chainlist)
print (longestchain)

def Prfix():
  if longestchain == 4:
    prefix = "But"
  elif longestchain == 5:
    prefix = "Pent"
  elif longestchain == 6:
    prefix = "Hex"
  elif longestchain == 7:
    prefix = "Hept"
  elif longestchain == 8:
    prefix = "Oct"
  return prefix

print (Prfix())