prefix to infix

[rontoto]

Hello, i have got a rpbolem with prefix to infix code.
I need to change this code, so it can work with input like this: +-4 2 3 or *4-2 3
and the output must be without useless parenthesis ............ 4-2+3 or 4*(2-3)
Can u help me please? Here is the code

class Calculator:
    def __init__ (self):
        self.stack = []

    def push (self, p):
        if p in ['+', '-', '*', '/']:
            op1 = self.stack.pop ()
            op2 = self.stack.pop ()
            self.stack.append ('(%s %s %s)' % (op1, p, op2) )
        elif p == '!':
            op = self.stack.pop ()
            self.stack.append ('%s!' % (op) )
        elif p in ['sin', 'cos', 'tan']:
            op = self.stack.pop ()
            self.stack.append ('%s(%s)' % (p, op) )
        else:
            self.stack.append (p)

    def convert (self, l):
        l.reverse ()
        for e in l:
            self.push (e)
        return self.stack.pop ()

c = Calculator ()