Merge pull request #2868 from takluyver/import-performance Import performance Defer various imports for a small reduction in startup time. IPython.lib.__init__ previously loaded IPython.lib.inputhook to export some of its functions. This meant that importing anything from IPython.lib also loaded inputhook. For now, I've just removed that import, but that is an API change, because the functions are no longer accessible as e.g. IPython.lib.enable_qt4 Added a note about the API change. Timing command, borrowed from Openoffice to simulate cold start: $ sync ; echo 3 | sudo tee /proc/sys/vm/drop_caches; time ipython3 -c pass Results with this branch: 7.68, 7.64, 7.35, 7.38 s 'real' Results with master: 8.17, 8.04, 7.81, 7.77