Pass by value for recursion?

I am trying to pass a parameter "by value". I have tried making a deep copy of the parameter that is passed recursively in order to prevent any changes from circling back to the parent function calls.

Here is a snippet of code that tries to generate the array of all possible parentheses.

def generateParenthesis(n):      #Iterate for each move.      M = 2 * n      retArray = []      def recHelper(numMoves, perm, stack):          print("Function call: ", numMoves, perm, stack)          newPerm = copy.deepcopy(perm)          newStack = stack.copy()          #Base case, no moves          if (numMoves == 0):              retArray.append(newPerm)              return            #Case when left move is valid          if (numMoves != len(newStack)):              #Apply the left move. Pass it recursively              newPerm +='('              #Update the stack accordingly              newStack.append('(')              #Decrease numMoves              newNumMoves = numMoves - 1              #Call it recursively              recHelper(newNumMoves, newPerm, newStack)          #Case when right move is valid          if len(newStack) != 0:              #Apply the right move. Pass it recursively              newPerm +=')'              #Update the stack accordingly, delete the top, last elm              newStack.pop()              #Decrease numMoves              newNumMoves = numMoves - 1              #Call it recursively              recHelper(newNumMoves, newPerm, newStack)          #done          return      recHelper(M, "", [])      return retArray  

Unfortunately, calling generateParenthesis(1) returns ['()','()(', '()()'] and not ['()'].

https://stackoverflow.com/questions/66739342/pass-by-value-for-recursion March 22, 2021 at 09:41AM