Python script to read a list of node pairs and output the list of node neighbors.

nodes.py

#!/usr/bin/env python3
# nodes <infile
#
# Read in lists of node neighbors, and output complete list of all neighbors
#
# Input:
#
# 0 1
# 1 2
# 2 3
# 3 4
# 4 0
# 4 1
# 5 3
#
# Output:
# [[1, 4], [0, 2, 4], [1, 3], [2, 4, 5], [0, 1, 3], [3]]

class NodeList:
  def __init__(self):
    self.nodes = {}

  def add_pair(self, n1, n2):
    self.add_node(n1, n2)
    self.add_node(n2, n1)

  def add_node(self, n1, n2):
    if n1 not in self.nodes:
      self.nodes[n1] = []
    if n2 not in self.nodes[n1]:    # add n2 only if not already a link
      self.nodes[n1].append(n2)

  def neighbors(self):
    return list(map(lambda k: sorted(self.nodes[k]), sorted(self.nodes.keys())))

nodes = NodeList()
while True:
  try:
    line = input()
    nums = [int(x) for x in line.split()]
    if len(nums) > 0:
      n1 = nums.pop(0)
      for nx in nums:
        nodes.add_pair(n1, nx)
  except EOFError:
    break

print(nodes.neighbors())

exit