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 (...). Typing an EOF (Control-D) at the primary prompt causes the interpreter to exit with a zero exit status.
The interpreter prints a welcome message stating its version number and a copyright notice before printing the first prompt, e.g.:
python Python 1.0.2 (May 3 1994) Copyright 1991-1994 Stichting Mathematisch Centrum, Amsterdam >>>