old_contents: import webapp2
  import os
  import jinja2
  
  template_dir = os.path.join(os.path.dirname(__file__), "templates")
  jinja_env = jinja2.Environment(loader = jinja2.FileSystemLoader(template_dir), autoescape  = True)
  
  
  class Handler(webapp2.RequestHandler):
      def write(self, *a, **kw):
          self.response.out.write(*a, **kw)
  
      def render_str(self, template, **params):
          t = jinja_env.get_template(template)
          return t.render(params)
  
      def render(self, template, **kw):
          self.write(self.render_str(template, **kw))
  
  class MainHandler(Handler):
      def get(self):
          self.render("input.html", title="calculator")
  
  class AnswerHandler(Handler):
  	def post(self):
  		num1 = self.request.get("num1")
  		opp = self.request.get("opp")
  		num2 = self.request.get("num2")
  		if num1 == "":
  			self.redirect("/error")
  		if num2 == "":
  			self.redirect("/error")
  		if opp == "+":
  			number = float(num1) + float(num2)
  		if opp == "-":
  			number = float(num1) - float(num2)
  		if opp == "*":
  			number = float(num1) * float(num2)
  		if opp == "/":
  			number = float(num1) / float(num2)
  		if opp == "**":
  			number = float(num1) ** float(num2)
  		self.render("answer.html", ans=number, title="answers")
  
  class ErrorHandler(Handler):
  	def get(self):
  		self.render("error.html")
  
  app = webapp2.WSGIApplication([
      ('/', MainHandler),
      ('/answer', AnswerHandler),
      ('/error', ErrorHandler)
  ], debug=True)
  
new_contents: import webapp2
  import os
  import jinja2
  
  template_dir = os.path.join(os.path.dirname(__file__), "templates")
  jinja_env = jinja2.Environment(loader = jinja2.FileSystemLoader(template_dir), autoescape  = True)
  
  
  class Handler(webapp2.RequestHandler):
      def write(self, *a, **kw):
          self.response.out.write(*a, **kw)
  
      def render_str(self, template, **params):
          t = jinja_env.get_template(template)
          return t.render(params)
  
      def render(self, template, **kw):
          self.write(self.render_str(template, **kw))
  
  class MainHandler(Handler):
      def get(self):
          self.render("input.html", title="calculator")
  
  class AnswerHandler(Handler):
  	def post(self):
  		num1 = self.request.get("num1")
  		opp = self.request.get("opp")
  		num2 = self.request.get("num2")
  		if num1 or num2 == "":
  			self.redirect("/error")
  		if num1 or num2 != "":
  			if opp == "+":
  				number = float(num1) + float(num2)
  			if opp == "-":
  				number = float(num1) - float(num2)
  			if opp == "*":
  				number = float(num1) * float(num2)
  			if opp == "/":
  				number = float(num1) / float(num2)
  			if opp == "**":
  				number = float(num1) ** float(num2)
  			self.render("answer.html", ans=number, title="answers")
  
  class ErrorHandler(Handler):
  	def get(self):
  		self.render("error.html")
  
  app = webapp2.WSGIApplication([
      ('/', MainHandler),
      ('/answer', AnswerHandler),
      ('/error', ErrorHandler)
  ], debug=True)
  
subject: fix bug with valadation