To quote the Emacs manual on The Init File:
When Emacs is started, it normally tries to load a Lisp program from an initialization file, or init file for short. This file, if it exists, specifies how to initialize Emacs for you. Emacs looks for your init file using the filenames
~/.emacs.d/init.el; you can choose to use any one of these three names. Here,
~/ stands for your home directory.
Originally, Emacs looked only for
~/.emacs. The variant names were introduced in more recent versions of Emacs.
So, in this case:
C-x C-f ~/.emacs <ENTER> to load or create your
(load-library “init_python”) into that file.
C-x C-s to save it.