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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _DecodeUrlSafe(urlsafe):
 """Decode a url-safe base64-encoded string. This returns the decoded string. """

  if not isinstance(urlsafe, basestring):
    raise TypeError('urlsafe must be a string; received %r' % urlsafe)
  if isinstance(urlsafe, unicode):
    urlsafe = urlsafe.encode('utf8')
  mod = len(urlsafe) % 4
  if mod:
    urlsafe += '=' * (4 - mod)
  # This is 3-4x faster than urlsafe_b64decode()
  return base64.b64decode(urlsafe.replace('-', '+').replace('_', '/'))