Return the "login name" of the user.

This function checks the environment variables:envvar:`LOGNAME`,

:envvar:`USER`,:envvar:`LNAME` and:envvar:`USERNAME`, in order, and

:envvar:`USER`,:envvar:`!LNAME` and:envvar:`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:mod:`pwd` module, otherwise, an exception is

Doc/library/functions.rst

Doc/library/functools.rst

Doc/library/getopt.rst

Doc/library/getpass.rst

Doc/library/gettext.rst

Doc/library/gzip.rst

Doc/library/http.client.rst