15.10. "getpass" — Portable password input
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The "getpass" module provides two functions:

getpass.getpass([prompt[, stream]])

   Prompt the user for a password without echoing.  The user is
   prompted using the string *prompt*, which defaults to "'Password:
   '". On Unix, the prompt is written to the file-like object
   *stream*.  *stream* defaults to the controlling terminal (/dev/tty)
   or if that is unavailable to "sys.stderr" (this argument is ignored
   on Windows).

   If echo free input is unavailable getpass() falls back to printing
   a warning message to *stream* and reading from "sys.stdin" and
   issuing a "GetPassWarning".

   在 2.5 版更改: The *stream* parameter was added.

   在 2.6 版更改: On Unix it defaults to using /dev/tty before falling
   back to "sys.stdin" and "sys.stderr".

   注解: If you call getpass from within IDLE, the input may be done
     in the terminal you launched IDLE from rather than the idle
     window itself.

exception getpass.GetPassWarning

   A "UserWarning" subclass issued when password input may be echoed.

getpass.getuser()

   Return the “login name” of the user.

   This function checks the environment variables "LOGNAME", "USER",
   "LNAME" and "USERNAME", in order, and returns the value of the
   first one which is set to a non-empty string.  If none are set, the
   login name from the password database is returned on systems which
   support the "pwd" module, otherwise, an exception is raised.
