Problem 1:
13

Problem 2:
5 4 3 2 1 

Problem 3:
{1, 2, 3, 4, 5}


Problem 4:
Gives an error

Problem 5:
{'a': 3, 'c': 4, 'd': 2}

6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 
E  B  B  A  D   D   C   A   C   A

For programming problems there are always a variety of possible solutions.

16.

An earlier posted solution had an unnecessary clause in this involving
isdigit.  That was relevant to an earlier version of this problem, but
not the current one.

def transformString( s ):
   if not s:
      return ""
   elif s[0].islower():
      return s[0].upper() + transformString( s[1:] )
   elif s[0].isupper():
      return s[0].lower() + transformString( s[1:] )
   else:
      return s[0] + transformString( s[1:] )

17. 

class ShoppingLine:
   def __init__( self, initialLine ):
      self.__line = initialLine

   def __len__( self ):
      count =  0
      for pair in self.__line:
         count += pair[1]
      return count

   def join( self, name, itemCount ):
      self.__line.append( (name, itemCount) )
   
   def checkout( self ):
      if not self.__line:
         return None
      else:
         name, count = self.__line.pop(0)
         return name

   def __str__( self ):
      out = "Line: " + str(self.__line)
      return out


   def __len__( self ):
      return len(self.__line)