permutations.py

def generate_subsets(i, sol, elements):
  # Base case
  if i == len(elements):
    # Print complete solution 
    print_subset_binary(sol, elements)
  else:
    # Generate candidate elements 
    for k in range(0, 2):
      # Include candidate in partial solution
      sol[i] = k
      # Expand partial solution at position i+1
      generate_subsets(i + 1, sol, elements)
      # Remove candidate from partial solution 
      sol[i] = None # optional

def generate_subsets_wrapper(elements ):
  sol = [None] * (len(elements))
  generate_subsets(0, sol, elements)
  
def print_subset_binary(sol, elements):
  no_elements = True
  print('{', end='')
  for i in range(0, len(sol)):
    if sol[i] == 1:
      if no_elements:
        print(elements[i], sep='', end='')
        no_elements = False 
      else:
        print(', ', elements[i], sep='', end='')
  print('}')

print(generate_subsets_wrapper(['a', 'b', 'c']))