Generate list of unique pairs (a, b) from N elements ensuring all elements participate in a and b.

generate-pairs-from-n-items.py

import sys, random

fout = open('pairs.txt', 'w')
# total number of people participating
total_people = int(sys.argv[1])

a, b = [], []

for i in xrange(1, total_people+1):
  a.append(i)
  while True:
    r = random.randint(1, total_people)
    if r not in b and r != i:
      b.append(r)
      break

for i, j in zip(a, b):
  fout.write(str(i)+" "+str(j)+"\n")
fout.close()