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I was taken back by this rather harsh treatment of Python.

Is it really realistic to 'have it all'? I'm fully aware that I'd have to go to crazier languages if I want parallelism or speed. For what Python is, it offers me reasonable tradeoffs (mostly slanted towards productivity)..

Regarding the FP comments, since it lacks TCO, my take away has always been that Python can only ever become a quasi-functional language. Its hard to be more than that in its current state.

Anyways. These questions made me want to ask you - what languages do you think are better in comparison?

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> I was taken back by this rather harsh treatment of Python.

I am taken aback by the evangelical tone of Python enthusiasts, where is has warts intentionally maintained by the creator in the form of missing features.

If you want speed you go to any other scripting language (other than Ruby). I agree Python is mostly sane and naiively productive. That being said, it's a result of the syntax. Transpiling it to another language like Google did, shows that the underlying technology is not worth much.

> what languages do you think are better in comparison

Better in what way? PHP, Go, Pony, Javascript all have these features and the problems with the languages are not that people don't understand when they come across a switch or map.

> If you want speed you go to any other scripting language (other than Ruby).

Ruby has historically had the same issues. Most Pythonistas I know aren't so evangelical. It's mostly a question of how to go about integrating C/C++ code.

Many people complaining about the GIL (and the like) have some naive microbenchmark, don't understand the trade-offs/limitations of their runtime etc. That doesn't mean critique isn't important and required, but it's going to be better when it's properly researched and improves on the body of work out there (https://www.youtube.com/watch?v=Obt-vMVdM8s).

> Transpiling it to another language like Google did, shows that the underlying technology is not worth much.

How is this any general indicator of the worth of the language?

It shows for some cases, that Google thought this was a worthwhile investment. Google has experimented for a long time with ways to improve how Python code can be run. They ran the Unladen Swallow project, but spent more time on LLVM issues at the time making it infeasible to continue the project.

They'll discontinue one path and try another. None of this is really a commentary from Google on CPython, the community, or the value that it has for most people. The people working on this stuff interact in a pretty friendly basis.

> If you want speed you go to any other scripting language (other than Ruby)

Which one? PHP? Perl? Bash? Scheme? VBScript? Windows PowerShell?

Python is in fact of the fastest scripting languages that exist, especially JIT'ed.

The notable exception is JS, and oh, that has a GIL too :P

The lack of tail-call optimization to make the CPython interpreter simpler and debugging easier by preserving the call stack. It was a choice, not an oversight.

Why not just make it a dev/production flag, then?

Probably because many tail-recursive functions _rely_ on tail-call elimination working reliably. Without also having an unbounded call stack, disabling tail-call elimination will likely just cause your programs to crash.

From a debugging viewpoint, this does not make sense, there is usually no interesting information in the in between frames.

TCE can also make debugging easier, how useful is a stack trace of 1000 lines consisting of

  ...
  File "bla.py", line 4, in fib
    return fib(n - 1) + fib(n - 2)
  File "bla.py", line 4, in fib
    return fib(n - 1) + fib(n - 2)
  File "bla.py", line 4, in fib
    return fib(n - 1) + fib(n - 2)

...

Not so much I think.

The notion that not having proper tail calls aids debugging always seemed like a post-hoc justification. The stack trace of an iterative function will lack exactly the same intermediate evaluation frames as a tail-recursive implementation.

The thing is, tail calls aren't _just_ about emulating iteration via recursion:

  def foo():
      raise ValueError

  def bar():
      return foo()

  bar()

With TCO, the stack trace would contain `main` and `foo`, as `bar`'s frame would be overwritten by `foo`. This example is simple, but `bar` could be a 50 line long if-else chain of tail calls and when debugging you won't necessarily know which condition was evaluated.

> The thing is, tail calls aren't _just_ about emulating iteration via recursion:

I completely agree, but there is also no need to perform TCO to make code like this safely runnable. TCO only becomes necessary/useful when implementing an iterative process where we can't statically know that the call stack won't be exhausted. That said, TCO is usually an all or nothing transformation, and it would be difficult to accurately avoid eliminating trivial tail calls like in your example.

A reasonable compromise might be for the Python VM to implement a TAIL_CALL bytecode op and require the programmer to decorate functions which rely on TCO. This wouldn't be any more onerous than manually trampolining large portions of code, which is the current method of getting around the lack of TCO.

A decorator that enabled TCO makes sense to me. Kind-of like the Numba project, it'd be a specialized JIT-compiler invoked only on some functions.

What's stopping that from being a 3rd-party library like Numba?

You can find simple decorators which try to provide space efficient tail recursion. Usually they work by trampolining the function. I've seen one example where a decorator rewrites the bytecodes to perform a goto in the case of self recursion. The problem is that all of these solutions are rather limited, easy to break, or have a pretty high runtime overhead. The general solution would be for a decorator to rewrite all CALL opcodes in tail postion to TAIL_CALL opcodes, but such an opcode currently does not exist. The actual implementation of a TAIL_CALL opcode would be almost idential to the CALL opcode, so adding it would probably be straightforward, but I'm speculating here.

I like how you picked an example that is explicitly not TCO-able.

In any case, this particular problem is no longer an issue as of Python 3.6, as that now collapses repeated stacktrace lines (see https://bugs.python.org/issue26823). Although this doesn't work for mutual tail calls, it does solve the debug noise issue in the most common case.

Ah yes, that is a bit stupid, I just wanted an example of a traceback :)

I never considered it harsh. If anything, it should be a testament to how nice Python is -- if I /didn't/ like it, I would have a much, much longer list of complaints!

People seem to be missing that sentiment -- I do love Python and use it almost daily. This is merely a list of thorns I run into frequently.

>Regarding the FP comments, since it lacks TCO, my take away has always been that Python can only ever become a quasi-functional language. Its hard to be more than that in its current state.

I mean, it could always encourage playing with functions more -- and importantly, providing an stdlib that encourages that.

>These questions made me want to ask you - what languages do you think are better in comparison?

That is a somewhat loaded question: my counter question would be, "In what regards?"

I cannot say a certain language is better than Python in every or most circumstances, but I can in regards to specific points/features, if you'd like to elaborate.

But it was harsh. You started the post with

> These are obvious flaws in design, in my opinion, that warrant re-looking at, but to which no real improvements are being made for some reason. (Incompetence? Politics? Both? Who knows.)

You list a number of things which Python ecosystem should do better or differently, and suggest that the reason why these changes aren't getting built as fast as you'd like is people playing politics or incompetence.

Whereas in reality, the two main reasons are that the changes will take lots of effort and time, which the volunteers don't have next to their day jobs (PyPy), or that the developers have different opinions on the ideal language design, and just don't agree with you (heavy functional programming).

"It is my personal subjective opinion that you are incompetent" isn't less harsh than "You are incompetent".

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