I am trying to obtain a dictionary that contains monomials (keys) and coefficients (values) for a multi-variate polynomial in SymEngine. This function exists in Symbolics.jl

This would be ungodly slow for univariate polynomials, and far worse for multi-variate ones.

SymEngine keeps an internal representation as a dictionary, I just cannot find much in terms of documentation on the package SymEngine.jl to know how to access it.

I had no idea that using symbolic systems there was also a need for speed.
However the function that finds the coefficients should not be much slower than diff() and subs()

I remember needing that too a while ago and I then went looking for it in the SymEngine repo. IIRC then the relevant function from SymEngine was/is not yet available via their C interface and one would need to make a PR in the C++ project first.
I ended up solving my problem in another way, so I did not follow up on that. But it would be great to add that functionality one day.

I see – do I understand correctly that the Julia wrappers are based on the C wrappers to the C++ project, but the Python wrappers are not based on the C wrappers?
If the C wrappers the Julia implementation are based on are these

then obtaining the dictionary of coefficients is not yet implemented, as far as I can tell. Thanks, this clarified things quite a bit.