all possible subsequences of a string in python

# Python3 program to print all Subsequences 
# of a string in iterative manner 
  
# function to find subsequence 
def subsequence(s, binary, length): 
    sub = "" 
    for j in range(length): 
          
        # check if jth bit in binary is 1 
        if (binary & (1 << j)): 
  
            # if jth bit is 1, include it 
            # in subsequence 
            sub += s[j] 
    return sub 
  
# function to print all subsequences 
def possibleSubsequences(s): 
  
    # map to store subsequence  
    # lexicographically by length 
    sorted_subsequence = {} 
  
    length = len(s) 
      
    # Total number of non-empty subsequence 
    # in string is 2^len-1 
    limit = 2 ** length 
      
    # i=0, corresponds to empty subsequence 
    for i in range(1, limit): 
          
        # subsequence for binary pattern i 
        sub = subsequence(s, i, length) 
          
        # storing sub in map 
        if len(sub) in sorted_subsequence.keys(): 
            sorted_subsequence[len(sub)] = \ 
             tuple(list(sorted_subsequence[len(sub)]) + [sub]) 
        else: 
            sorted_subsequence[len(sub)] = [sub] 
  
    for it in sorted_subsequence: 
          
        # it.first is length of Subsequence 
        # it.second is set<string> 
        print("Subsequences of length =", it, "are:") 
        for ii in sorted(set(sorted_subsequence[it])): 
              
            # ii is iterator of type set<string> 
            print(ii, end = ' ') 
        print() 
  
# Driver Code 
s = "aabc"
possibleSubsequences(s) 
  
# This code is contributed by ankush_953