I'm stumped by this seemingly trivial problem...

I would like to use python to take a string of numbers ("123" for example) and create a list that has all possible expressions where a "+" or "-" (or nothing at all) can be inserted between any numbers.

For the example "123" the list would be:

["123","12+3","12-3","1+23","1+2+3","1+2-3","1-23","1-2+3","1-2-3"]

If the length of the string of numbers is N, then the list should contain 3^(N-1) strings.

I feel like this should be done recursively, but I'm stuck trying to figure out how to return the 3 different options (+,-,None).

I believe that the base case of the function should be:

def options(string):
  if len(string) == 1:
    return string
  else:
    #This is where I am stuck
python string recursion
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