Re: Python REPL using standard library functions

[Dmitry Gutov]

On 02.11.2020 13:40, Yuri Khan wrote:
> On Mon, 2 Nov 2020 at 16:50, Dmitry Gutov <dgutov@yandex.ru> wrote:
> > On 02.11.2020 08:14, Yuri Khan wrote:
> > > Python has ast.parse(), compile() and exec(), all three exposed in the
> > > standard library.
> >
> > I'd be willing to bet that any given Python REPL doesn't use them, though.
>
> One of the guiding principles of Python is “There must be one — and
> preferably only one — obvious way to do it”. Implementing a REPL in
> terms of ast.parse, compile() and exec is one obvious way to do it.
> There is a catch that compile() with an option argument can be used
> instead of ast.parse, so that’s another obvious way to do it. Both are
> fully exposed to the user though.

Is eval implemented in terms of either?

> Indeed, my limited experimentation shows I can augment these built-in
> functions and they are immediately picked up by at least one REPL:

The basic Python REPL doesn't seem to use it (your experiment doesn't 
result in anything being printed). Perhaps ipython uses ast.parse for 
syntax highlighting?

Ruby's standard library also includes a parser. The 'eval' method 
doesn't seem to be implemented in terms of it. At least, not directly.

In any case, I disagree that whether something is a REPL or not, should 
be decided by its implementation details.