problema 3 e 4

def sub(str):
#@ param str: string
  str0=''
  for ch in str:
    if ch in str0 and ch !=' ':
      str0=str0+'*'
    else:
      str0=str0+ch
  return str0


def palindroma(str):
#@ param str: string
  i=0
  while i<=(len(str)/2):
    if not str[i]==str[(len(str)-1)-i]:
      return False
    i=i+1
  return True