code: def GetRealPath(filename):
    
    if os.path.isabs(filename):                # already absolute
      return filename
  
    if filename.startswith('./') or  filename.startswith('../'): # relative
      return os.path.abspath(filename)
  
    path = os.getenv('PATH', '')
    for directory in path.split(':'):
      tryname = os.path.join(directory, filename)
      if os.path.exists(tryname):
        if not os.path.isabs(directory):  # relative directory
          return os.path.abspath(tryname)
        return tryname
    if os.path.exists(filename):
      return os.path.abspath(filename)
    return None
docs: Given an executable filename, find in the PATH or find absolute path.
    Args:
      filename  An executable filename (string)
    Returns:
      Absolute version of filename.
      None if filename could not be found locally, absolutely, or in PATH