When commands are read from a tty, the interpreter is said to be in interactive mode. In this mode it prompts for the next command with the primary prompt, usually three greater-than signs (">>> "); for continuation lines it prompts with the secondary prompt, by default three dots ("... ").
The interpreter prints a welcome message stating its version number and a copyright notice before printing the first prompt, e.g.:
python Python 1.5b1 (#1, Dec 3 1997, 00:02:06) [GCC 126.96.36.199] on sunos5 Copyright 1991-1995 Stichting Mathematisch Centrum, Amsterdam >>>