code: def guess_filename(filename):
      
      if osp.isfile(filename):
          return filename
      if not filename.endswith('.py'):
          filename += '.py'
      for path in [getcwd_or_home()] + sys.path:
          fname = osp.join(path, filename)
          if osp.isfile(fname):
              return fname
          elif osp.isfile(fname+'.py'):
              return fname+'.py'
          elif osp.isfile(fname+'.pyw'):
              return fname+'.pyw'
      return filename
docs: Guess filename