It appears simple on the surface, it is as complex as Common Lisp or C++, when one starts exploring the language surface, runtime capabilities, and standard library.
As an experienced Python programmer who has dabbled in C++ (and Rust), I find this claim very dubious, though I can't say either way about Common Lisp. The difficult parts of Python-the-language (e.g. metaclasses) are both fairly easily to explain and also so rarely used even by library authors that explanation isn't usually necessary.
I suppose the standard library can be considered complex, but is hardly worse than C++.
I've seen plenty of non-programmers become proficient enough in Python to be productive, but maybe one guy -- a statistician maintaining R libraries -- learn enough C++ to be dangerous.
How much would you score on a Python pub quiz, including all versions of Python between 1.6 and 3.10?
Questions would include changes across minor versions, meta programming, old and new classes, ABC, slots, magical methods, async, standard library, famous libraries like stackless, ...
Outside of tiny niches the world is on Python 3 now, so I don't think older versions are particularly relevant when evaluating how complex Python is. For that reason old vs new style classes don't cause issues. Nor do the existence of niche implementations like Stackless, unless we want to also claim such implementations as sources of complexity for C++ or (especially) Common Lisp, at which point it's a wash.
Having trained many newly-graduated data scientists and engineers to a level of being reasonably productive in Python, my assessment is that it is simply not that difficult to get a handle on. But if I'm expected to take non-career-programmers to comparable C++ fluency, that would be a considerably longer process.
Things they'd have to worry about in C++ that they don't have to worry about in Python: memory leaks, memory debugging, complex templates, libraries written in the lowest-level way possible, move semantics, ...
