import re


def xisabs(filename):
  """ Cross-platform version of `os.path.isabs()`
      Returns True if `filename` is absolute on
      Linux, OS X or Windows.
  """
  if filename.startswith('/'):     # Linux/Unix
    return True
  elif filename.startswith('\\'):  # Windows
    return True
  elif re.match(r'\w:[\\/]', filename): # Windows
    return True
  return False