Command Line Calendar Project: edits event name instead of event date

Somehow, my code edits the event name to a new date instead of editing the event date. How can I change the code so it doesn’t leave me with an event name + the updated event date? This is my current code:

from time import sleep, strftime

USER_FIRST_NAME = "Erin"
calendar = {}
def welcome():
  print "Welcome, " + USER_FIRST_NAME + "."
  print "Looking for appointments"
  sleep(1)
  print "Today is " + strftime("%A, %B, %d, %Y")
  print "It's " + strftime("%H, %M, %S")
  sleep(1)
  print "What would you like to do?"

def start_calendar():
  welcome()
  start = True
  while start:
    user_choice = raw_input("A to Add, U to Update, V to View, D to Delete, X to Exit: ")
    user_choice = user_choice.upper()
    if user_choice == "V":
      if len(calendar.keys()) < 1:
        print "Calendar is empty."
      else:
        print calendar
    elif user_choice == "U":
      date = raw_input("What date? ")
      update = raw_input("Enter the update: ")
      calendar[date] = update
      print "Calendar is updated successfully"
      print calendar
    elif user_choice == "A":
      event = raw_input("Enter event: ")
      date = raw_input("Enter date (MM/DD/YYYY): ")
      if len(date) > 10 or int(date[6:] < int(strftime("%Y"))):
        print "invalid date"
        try_again = raw_input("Try again? Y for Yes, N for No: ")
        try_again = try_again.upper()
        if try_again == "Y":
          continue
        else:
          start = False
      else:
        calendar[date] = event
        print calendar
    elif user_choice == "D":
      if len(calendar.keys()) < 1:
        print "Calender is already empty."
      else: 
        event = raw_input("What event?")
        for date in calendar.keys():
          if event == calendar[date]:
            del calendar[date]
            print "Event deleted successfully"
            print calendar
          else:
            print "Event invalid"
    elif user_choice == "X":
      start = False
    else:
      print "I don't understand, I'm leaving"
      start = False

start_calendar()