title: TypeError: Object of type 'function' has no len() in python
body: <p>I am writing a program with python which will do several things such as login as student, login as driver. but when I try to run the code, I face several problems. I am writting down the code below. and also I am giving you the screenshot of the errors. Please help if you can.</p>
  
  <p>Thanks in advance.</p>
  
  <pre><code> print "========================================================"
   print "==============Welcome to LiftServer System=============="
   print "========================================================"
   print "\n"
   print "Type start() to View the Options"
   print "\n"
  
  
  
   DriverLogin=[("ali", "ila"), ("bla", "alb")]
   PassLogin=[("ila", "ali")]
  
  
   def CorrectDriverLogin(n,x):
    for i in range (len(x)):
      a,b = x[i]
      if (a==n):
          return b
  
   def CorrectPassLogIn(c,y):
    for j in range (len(y)):
       d,e = y[j]
       if (d==c):
          return e
  
  
   def start():
    print "\n"
    print "=====================You are in the System============="
    print "\n"
    print "Choose an option:"
    print "======================================================="
    print "1. Login for Drivers"
    print "2. Login for Students"
    print "3. Exit"
    print "======================================================="
    print "\n"
    choice= raw_input("Enter the choice number:")
    print "\n"
  
    if (int(choice)==1):
      print""
      DriverLogin()
  
    elif(int(choice)==2):
      print ""
      PassLogin()
  
    if (int(choice)==1):
      print" "
      print" "
      p = raw_input (" Current campus: ")
      k = raw_input (" Travelling to: ")
      m = raw_input (" Leaving Time: ")
      x = raw_input (" Enter AM / PM: ")
      a = raw_input (" Number of available seats: ")
      j = raw_input (" Meeting time: ")
      print" \nI am in campus " + p + " ,leaving to campus " + k + " at: " + m + x +" ,where I have only " + a + " seat(s) available."
      print" "
      print"I will be at the reception at: " + j + x + "."
      print" "    
      print"===================================================="
      print"\n"
      print "Send message? "
      print" "
      sendTheMessageD()
  
  elif (int(choice)==2):
      homePage()
  
   def sendTheMessageD():
      print" "
      print"1. Yes"
      print"2. No"
      choice = raw_input ("Confirm: ")
      print" "
      homePage()
  
   def PassLogin():
       userPass = raw_input("Username:")
       passName = raw_input("Password:")
       choice=0
       if (userPass==CorrectPassLogIn(passName, PassLogin)):
         print"\n"
         print "=================================================================="
         print "1. Send a Message"
         print "2. View Messages"
         print "3. Log out of the System"
         print "==================================================================="
         print "\n"
         choice = raw_input("Enter the choice's number:")
         print"\n"
       else:
          print"Incorrect Username or Password"
          print"\n"
          print"Try To Log In Again"
  
       if (int(choice)==1):
          print" "
          sendMessageP()
  
       elif(int(choice)==2):
          print" "
          viewMessageD()
    def sendMessageP():
          print "======================================================================="
          print "1)Write a message"
          print "2)Go Back"
          print "===========++=========================================================="
          print" "
          choice = raw_input("Enter The choice's Number: ")
  
        if(int(choice)==1):
          print" "
          y = raw_input("Destination: ")
          c = raw_input("Time: ")
          l = raw_input("Enter AM ? PM: ")
          t = raw_input("Required seats: ")
          print"\n Is there anyone going to campus " + y + " ,at: " + c + l + " ,and has " + t + " seat(s) available."
  
        elif(int(choice)==2):
          print""
          def sendTheMessageP():
          print" "
          print"1)Yes"
          print"2)No"
          choice = raw_input ("confirm")
          print" "
          homePage()
      def viewMessageD():
          print "======================================================================="
          print"Inbox"
          print" "
          print"1. Message 1"
          print"2. Message 2"
          print "======================================================================="
          choice = raw_input ("Enter the choice's Number:")
  
        if(int(choice)==1):
          print"\n Message 1 is viewed"
          if(int(choice)==2):
          print"\n Message 2 is viewed"
        else:
          print""
  
      def DriverLogin():
          xdriver = raw_input("Username:")
          xpass = raw_input("Password:")
          choice =0
        if (xpass==CorrectDriverLogin(xdriver, DriverLogin)):
          print"\n"
          print "============= You are now Logged in as a Driver ================"
          print"Choose an option:-"
          print "======================================================================"
          print "1. Send a Message"
          print "2. View Messages"
          print "3. Log out of the system"
          print "======================================================================"
          print "\n"
          choice = raw_input("Enter the choice's Number:")
        else:
          print"\n"
          print"Incorrect Username or Password"
          print"\n"
          print"You are logged out of the System Try To Log In Again Please"
  
        if(int(choice)==1):
          print" "
          sendMessageD()
  
        elif(int(choice)==2):
          print" "
  
        elif(int(choice)==3):
          print" "
  
      def homePage():
          print"\n"
          print "======================================================================="
          print "1. Send a Message"
          print "2. View Messages"
          print "3. Log Out of the System"
          print "======================================================================="
          print "\n"
          choice = raw_input("Enter the Choice's Number:")
  
      def sendMessageD():
          print "======================================================================="
          print"1. Write your message"
          print"2. Go Back"
          print "======================================================================="
          print" "
          choice = raw_input("Enter The Choice's Number:")
  </code></pre>
  
  <p>And here is the error I am getting:
  <img src="https://i.stack.imgur.com/zZwql.jpg" alt="enter image description here"></p>