Combinations in Python without using itertools

# Import combinations from itertools
from itertools import combinations 
  
    
def n_length_combo(arr, n): 
    
    # using set to deal 
    # with duplicates  
    return list(combinations(arr, n)) 
  
# Driver Function 
if __name__ == "__main__": 
    arr = 'abc' 
    n = 2
    print (n_length_combo([x for x in arr], n) )

# Function to create combinations 
# without itertools
def n_length_combo(lst, n):
    
    if n == 0:
        return [[]]
    
    l =[]
    for i in range(0, len(lst)):
        
        m = lst[i]
        remLst = lst[i + 1:]
        
        remainlst_combo = n_length_combo(remLst, n-1)
        for p in remainlst_combo:
             l.append([m, *p])
          
    return l

# Driver code
if __name__=="__main__":
    arr ="abc"
    print(n_length_combo([x for x in arr], 2))

import numpy


def n_length_combo(iterable, r):
    
    char = tuple(iterable)
    n = len(char)
    
    if r > n:
        return
    
    index = numpy.arange(r)
    
    # returns the first sequence 
    yield tuple(char[i] for i in index)
    
    while True:
        
        for i in reversed(range(r)):
            if index[i] != i + n - r:
                break
        else:
            return
        
        index[i] += 1
        
        for j in range(i + 1, r):
            
            index[j] = index[j-1] + 1
            
        yield tuple(char[i] for i in index)
        
# Driver code
print([x for x in n_length_combo("abc", 2)])