RPM's macro expansion has a maximum depth of 16.
I'm now playing a kind of code golf, to fit as much expansion into these 16 levels.

The problem: with "%define pythons python2 python3 pypy3", expand "%{python_module foo}" => "python2-foo python3-foo pypy3-foo".
This must fit into one line and can't use shell or Lua, because it also targets a non-RPM spec parser that doesn't have these features.
Fit as many pythons as you can!

my current solution:

%python_module_iter(a:) %{-a*}-%{args} %{expand:%%{?!python_module_iter_%1:%%{python_module_iter -a %*}}}
%python_module_iter_STOP stop

%python_module() %{expand:%%define args %{**}} %{expand:%%{python_module_iter -a %{pythons} STOP}}

At four pythons, this is 14 levels deep. 3 levels per python, 2 for setup.
now the question is: can I fit one more?

I *could* get to 2 levels per python, if i didn't mind that the recursion never stops....

...which doesn't actually matter in RPM. It's some sort of error somewhere in the log, but the output is the right thing.