How to access bash completion (for a particular program or all programs) from within a bash or Python script?

Question

If I read user input via bash with read -e or via Python with input(), is there a way to give the user access to a particular program's bash completion when they press Tab? For example, to give the user access to git's bash completion, so that if they type com<Tab> within the read -e prompt, it should complete to commit.

Alternatively, is there a way to simply give the user access to ALL bash autocompletion? E.g. if they type git com<Tab>, it should complete to git commit, or if they type ech<Tab> it should complete to echo.