Good to know - I guess in most circumstances copy-and-paste already works, because the input will be arriving via a line-buffered IO stream.
I was thinking that with #16649 implemented, it would be possible to simply switch from "single" to "exec", without users needing to request the multi-statement support explicitly. However, I'm now back to wondering if such a change might have a few unforeseen consequences I haven't thought of.
So if that seems like too much of a risk to backwards compatibility, how about moving the "symbol" argument to __init__, rather than needing to supply it with each call to push?