Python code to generate all subsets of a set.

allsubsets.py

"""
Generate all subsets of a set using recursion
"""
def subsets1(S):
  if S == []:
    return [[]]
  
  result = [[]]
  n = len(S)
  visited = [False] * n
  
  def recurse(i, n, li):
    if i == n:
      return
    
    if len(li) > 0:
      result.append([x for x in li])
    
    for j in range(i, n):
      if visited[j]:
        continue
      visited[j] = True
      li.append(S[j])
      recurse(j, n, li)
      li.pop()
      visited[j] = False
      
  recurse(0, n, [])
  return result

"""
Generate all subsets of a set without using recursion
"""
def subsets2(S):
  if S == []:
    return [[]]

  result = [[]]

  while len(S):
    temp_r = []
    x = S.pop()
    for r in result:
      temp_r.append(r + [])
      temp_r.append(r + [x])

    result = [item for item in temp_r]

  return result


if __name__ == "__main__":
  print(subsets1([1, 2, 3]))
  print(subsets2([1, 2, 3]))