removeAlpha/Digit con for e while

def removeAlpha_for(seqch):
# @param seqch: String
# return string
  new_string = ""
  for s in range(len(seqch)):
    if not seqch[s].isalpha():
      new_string +=seqch[s]
  return new_string

def removeDigit_for(seqch):
# @param seqch: String
# return string
  new_string = ""
  for s in range(len(seqch)):
    if not seqch[s].isalpha():
      new_string += seqch[s]
  return new_string

def removeAlpha_while(seqch):
# @param seqch: String
# return string
  s = 0
  new_string = ""
  while s < len(seqch):
    if not seqch[s].isalpha():
      new_string += seqch[s]
    s += 1
  return new_string

def removeDigit_while(seqch):
# @param seqch: String
# return string
  s = 0
  new_string = ""
  while s < len(seqch):
    if not seqch[s].isdigit():
      new_string += seqch[s]
    s += 1
  return new_string