1) Triangular number can be easily got as i*(i+1)//2 for i=1,2,... sample code: [i*(i+1)//2 for i in range(n)] 2) Sorting in python is easy. Just use sorted() 3( You don't need temporary variable to swap the value. Use a,b=b,a for example. More

It7s convenient to use the parameter "key" of the function "sorted." It specifies how it is sorted, not affecting the resulting list. More

The module "itertools" has "combinations" and "permutations" http://docs.python.org/2/library/itertools.html More

the "replace" method of string class is convenient. Try "abc def gh".replace(" ","") for example. More