In both languages threads are an added after-thought and no, I disagree with you - multithreading is not an implementation detail. For example, why do you think classes in Java are immutable?
Also, I consider the standard library to be a part of the core language, because it is. Python doesn't have many concurrency primitives that are commonly used in Java, even really common ones, like AtomicReference or CountDownLatch. Heck, it doesn't even have volatile variables, let alone ForkJoinPool or other niceties. What's actually in the standard library? Well, the multiprocessing library is now baked in for doing "process-based threading", which really means stuff based on fork() that is unportable, because the language implementors gave up on threads a long time ago.
It doesn't stop at concurrency primitives though. For example Python has the notion of destructors in the language, the reference implementation having a GC based on reference counting, so when implementing it on top of the JVM/CLR or whatever platform that doesn't do reference counting, that's at least one feature that can't work.
Add to that libraries like NumPy/Scipy that are basically unportable, or Django that says it runs on Jython but nobody mentions that Django needs the MySQL client written in C and won't work with the pure version, or the myriad other libraries in the ecosystem all written for CPython and expecting a GIL. Anybody that is fantasizing about Python having a usable implementation other than CPython is delusional.
> In both languages threads are an added after-thought
So?
> no, I disagree with you - multithreading is not an implementation detail.
Threading is a language feature, not an implementation detail. Whether threads are implemented by way of native threads on the underlying platform (as in JRuby, current CPython or MRI), or green threads in the runtime (as in old MRI, etc.), and, in the latter case, whether the green threads are mapped to native threads on an N:1 (as in old MRI) or M:N (as in the main Erlang implementation) model are implementation details.
> For example Python has the notion of destructors in the language, the reference implementation having a GC based on reference counting, so when implementing it on top of the JVM/CLR or whatever platform that doesn't do reference counting, that's at least one feature that can't work.
Sure, it could, since you could obviously (at the cost of making interop harder) write a Python implementation with its own garbage collector that ran on the JVM or CLR. You might choose to sacrifice portability for better interop with the languages the platform was designed for, but that's a choice.
> Django that says it runs on Jython but nobody mentions that Django needs the MySQL client written in C and won't work with the pure version
Seems to me that's a problem either with Django or the pure python MySQL driver, but not with the Python language.
> Anybody that is fantasizing about Python having a usable implementation other than CPython is delusional.
Perhaps; I'm less familiar with Python's other implementations than with Ruby's (particular JRuby) which is definitely usable, and definitely uses native threads without a GIL.
Also, I consider the standard library to be a part of the core language, because it is. Python doesn't have many concurrency primitives that are commonly used in Java, even really common ones, like AtomicReference or CountDownLatch. Heck, it doesn't even have volatile variables, let alone ForkJoinPool or other niceties. What's actually in the standard library? Well, the multiprocessing library is now baked in for doing "process-based threading", which really means stuff based on fork() that is unportable, because the language implementors gave up on threads a long time ago.
It doesn't stop at concurrency primitives though. For example Python has the notion of destructors in the language, the reference implementation having a GC based on reference counting, so when implementing it on top of the JVM/CLR or whatever platform that doesn't do reference counting, that's at least one feature that can't work.
Add to that libraries like NumPy/Scipy that are basically unportable, or Django that says it runs on Jython but nobody mentions that Django needs the MySQL client written in C and won't work with the pure version, or the myriad other libraries in the ecosystem all written for CPython and expecting a GIL. Anybody that is fantasizing about Python having a usable implementation other than CPython is delusional.