Built-in global variables

:stdin
:stdout
:stderr
File objects used for standard input, output and errors:

• :stdin

  is used for all interactive input (including calls to

  input()

  );

• :stdout

  is used for the output of

  print()

  ;
• error messages go to

  :stderr

  .

:argv
The array of command-line arguments.

:argv[0]

is the executable name.
It can be accessed only when there is a

:start:

marker present in the source code.
(

:start:

marker is an analogue of Python's

if __name__ == '__main__'

and is used to denote code which shouldn't be executed when this source file is imported from another source file (see this example).)