userinput=''
result=''
while userinput not in ['.','!','?']:
  userinput = raw_input('Enter a word . ! or ? to end):')
  result+=" "+userinput
else:
  print result
    

Enter a word . ! or ? to end):My
Enter a word . ! or ? to end):Name
Enter a word . ! or ? to end):is 
Enter a word . ! or ? to end):Walter
Enter a word . ! or ? to end):White
Enter a word . ! or ? to end):!!
Enter a word . ! or ? to end):!
 My Name is  Walter White !! !