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Paul Boddie's Free Software-related blog » English: Some Thoughts on Python-Like Languages

A few different things have happened recently that got me thinking about writing something about Python, its future, and Python-like languages. I don’t follow the different Python implementations as closely as I used to, but certain things did catch my attention over the last few months. But let us start with things closer to the present day.

I was neither at the North American PyCon event, nor at the invitation-only Python Language Summit that occurred as part of that gathering, but LWN.net has been reporting the proceedings to its subscribers. One of the presentations of particular interest was covered by LWN.net under the title “Keeping Python competitive”, apparently discussing efforts to “make Python faster”, the challenges faced by different Python implementations, and the limitations imposed by the “canonical” CPython implementation that can frustrate performance improvement efforts.

Here is where this more recent coverage intersects with things I have noticed over the past few months. Every now and again, an attempt is made to speed Python up, sometimes building on the CPython code base and bolting on additional technology to boost performance, sometimes reimplementing the virtual machine whilst introducing similar performance-enhancing technology. When such projects emerge, especially when a large company is behind them in some way, expectations of a much faster Python are considerable.

Thus, when the Pyston reimplementation of Python became more widely known, undertaken by people working at Dropbox (who also happen to employ Python’s creator Guido van Rossum), people were understandably excited. Three years after that initial announcement, however, and those ambitious employees now have to continue that work on their own initiative. One might be reminded of an earlier project, Unladen Swallow, which also sought to perform just-in-time compilation of Python code, undertaken by people working at Google (who also happened to employ Python’s creator Guido van Rossum at the time), which was then abandoned as those people were needed to go and work on other things. Meanwhile, another apparently-broadly-similar project, Pyjion, is being undertaken by people working at Microsoft, albeit as a “side project at work”.

As things stand, perhaps the most dependable alternative implementation of Python, at least if you want one with a just-in-time compiler that is actively developed and supported for “production use”, appears to be PyPy. And this is only because of sustained investment of both time and funding over the past decade and a half into developing the technology and tracking changes in the Python language. Heroically, the developers even try and support both Python 2 and Python 3.

Motivations for Change

Of course, Google, Dropbox and Microsoft presumably have good reasons to try and get their Python code running faster and more efficiently. Certainly, the first two companies will be running plenty of Python to support their services; reducing the hardware demands of delivering those services is definitely a motivation for investigating Python implementation improvements. I guess that there’s enough Python being run at Microsoft to make it worth their while, too. But then again, none of these organisations appear to be resourcing these efforts at anything close to what would be marshalled for their actual products, and I imagine that even similar infrastructure projects originating from such companies (things like Go, for example) have had many more people assigned to them on a permanent basis.

And now, noting the existence of projects like Grumpy – a Python to Go translator – one has to wonder whether there isn’t some kind of strategy change afoot: that it now might be considered easier for the likes of Google to migrate gradually to Go and steadily reduce their dependency on Python than it is to remedy identified deficiencies with Python. Of course, the significant problem remains of translating Python code to Go and still have it interface with code written in C against Python’s extension interfaces, maintaining reliability and performance in the result.

Indeed, the matter of Python’s “C API”, used by extensions written in C for Python programs to use, is covered in the LWN.net article. As people have sought to improve the performance of their software, they have been driven to rewrite parts of it in C, interfacing these performance-critical parts with the rest of their programs. Although such optimisation techniques make sense and have been a constant presence in software engineering more generally for many decades, it has almost become the path of least resistance when encountering performance difficulties in Python, even amongst the maintainers of the CPython implementation.

And so, alternative implementations need to either extract C-coded functionality and offer it in another form (maybe even written in Python, can you imagine?!), or they need to have a way of interfacing with it, one that could produce difficulties and impair their own efforts to deliver a robust and better-performing solution. Thus, attempts to mitigate CPython’s shortcomings have actually thwarted the efforts of other implementations to mitigate the shortcomings of Python as a whole.

Is “Python” Worth It?

You may well be wondering, if I didn’t manage to lose you already, whether all of these ambitious and brave efforts are really worth it. Might there be something with Python that just makes it too awkward to target with a revised and supposedly better implementation? Again, the LWN.net article describes sentiments that simpler, Python-like languages might be worth considering, mentioning the Hack language in the context of PHP, although I might also suggest Crystal in the context of Ruby, even though the latter is possibly closer to various functional languages and maybe only bears syntactic similarities to Ruby (although I haven’t actually looked too closely).

One has to be careful with languages that look dynamic but are really rather strict in how types are assigned, propagated and checked. And, should one choose to accept static typing, even with type inference, it could be said that there are plenty of mature languages – OCaml, for instance – that are worth considering instead. As people have experimented with Python-like languages, others have been quick to criticise them for not being “Pythonic”, even if the code one writes is valid Python. But I accept that the challenge for such languages and their implementations is to offer a Python-like experience without frustrating the programmer too much about things which look valid but which are forbidden.

My tuning of a Python program to work with Shedskin needed to be informed about what Shedskin was likely to allow and to reject. As far as I am concerned, as long as this is not too restrictive, and as long as guidance is available, I don’t see a reason why such a Python-like language couldn’t be as valid as “proper” Python. Python itself has changed over the years, and the version I first used probably wouldn’t measure up to what today’s newcomers would accept as Python at all, but I don’t accept that the language I used back in 1995 was not Python: that would somehow be a denial of history and of my own experiences.

Could I actually use something closer to Python 1.4 (or even 1.3) now? Which parts of more recent versions would I miss? And which parts of such ancient Pythons might even be superfluous? In pursuing my interests in source code analysis, I decided to consider such questions in more detail, partly motivated by the need to keep the investigation simple, partly motivated by laziness (that something might be amenable to analysis but more effort than I considered worthwhile), and partly motivated by my own experiences developing Python-based solutions.

A Leaner Python

Usually, after a title like that, one might expect to read about how I made everything in Python statically typed, or that I decided to remove classes and exceptions from the language, or do something else that would seem fairly drastic and change the character of the language. But I rather like the way Python behaves in a fundamental sense, with its classes, inheritance, dynamic typing and indentation-based syntax.

Other languages inspired by Python have had a tendency to diverge noticeably from the general form of Python: Boo, Cobra, Delight, Genie and Nim introduce static typing and (arguably needlessly) change core syntactic constructs; Converge and Mython focus on meta-programming; MyPy is the basis of efforts to add type annotations and “optional static typing” to Python itself. Meanwhile, Serpentine is a project being developed by my brother, David, and is worth looking at if you want to write software for Android, have some familiarity with user interface frameworks like PyQt, and can accept the somewhat moderated type discipline imposed by the Android APIs and the Dalvik runtime environment.

In any case, having already made a few rounds trying to perform analysis on Python source code, I am more interested in keeping the foundations of Python intact and focusing on the less visible characteristics of programs: effectively reading between the lines of the source code by considering how it behaves during execution. Solutions like Shedskin take advantage of restrictions on programs to be able to make deductions about program behaviour. These deductions can be sufficient in helping us understand what a program might actually do when run, as well as helping the compiler make more robust or efficient programs.

And the right kind of restrictions might even help us avoid introducing more disruptive restrictions such as having to annotate all the types in a program in order to tell us similar things (which appears to be one of the main directions of Python in the current era, unfortunately). I would rather lose exotic functionality that I have never really been convinced by, than retain such functionality and then have to tell the compiler about things it would otherwise have a chance of figuring out for itself.

Rocking the Boat

Certainly, being confronted with any list of restrictions, despite the potential benefits, can seem like someone is taking all the toys away. And it can be difficult to deliver the benefits to make up for this loss of functionality, no matter how frivolous some of it is, especially if there are considerable expectations in terms of things like performance. Plenty of people writing alternative Python implementations can attest to that. But there are other reasons to consider a leaner, more minimal, Python-like language and accompanying implementation.

For me, one rather basic reason is merely to inform myself about program analysis, figure out how difficult it is, and hopefully produce a working solution. But beyond that is the need to be able to exercise some level of control over the tools I depend on. Python 2 will in time no longer be maintained by the Python core development community; a degree of agitation has existed for some time to replace it with Python 3 in Free Software operating system distributions. Yet I remain unconvinced about Python 3, particularly as it evolves towards a language that offers “optional” static typing that will inevitably become mandatory (despite assertions that it will always officially be optional) as everyone sprinkles their code with annotations and hopes for the magic fairies and pixies to come along and speed it up, that latter eventuality being somewhat less certain.

There are reasons to consider alternative histories for Python in the form of Python-like languages. People argue about whether Python 3′s Unicode support makes it as suitable for certain kinds of programs as Python 2 has been, with the Mercurial project being notable in its refusal to hurry along behind the Python 3 adoption bandwagon. Indeed, PyPy was devised as a platform for such investigations, being only somewhat impaired in some respects by its rather intensive interpreter generation process (but I imagine there are ways to mitigate this).

Making a language implementation that is adaptable is also important. I like the ability to be able to cross-compile programs, and my own work attempts to make this convenient. Meanwhile, cross-building CPython has been a struggle for many years, and I feel that it says rather a lot about Python core development priorities that even now, with the need to cross-build CPython if it is to be available on mobile platforms like Android, the lack of a coherent cross-building strategy has left those interested in doing this kind of thing maintaining their own extensive patch sets. (Serpentine gets around this problem, as well as the architectural limitations of dropping CPython on an Android-based device and trying to hook it up with the different Android application frameworks, by targeting the Dalvik runtime environment instead.)

No Need for Another Language?

I found it depressingly familiar when David announced his Android work on the Python mobile-sig mailing list and got the following response:

In case you weren't aware, you can just write Android apps and services
in Python, using Kivy.  No need to invent another language.

Fortunately, various other people were more open-minded about having a new toolchain to target Android. Personally, the kind of “just use …” rhetoric reminds me of the era when everyone writing Web applications in Python were exhorted to “just use Zope“, which was a complicated (but admittedly powerful and interesting) framework whose shortcomings were largely obscured and downplayed until enough people had experienced them and felt that progress had to be made by working around Zope altogether and developing other solutions instead. Such zero-sum games – that there is one favoured approach to be promoted, with all others to be terminated or hidden – perhaps inspired by an overly-parroted “only one way to do it” mantra in the Python scene, have been rather damaging to both the community and to the adoption of Python itself.

Not being Python, not supporting every aspect of Python, has traditionally been seen as a weakness when people have announced their own implementations of Python or of Python-like languages. People steer clear of impressive works like PyPy or Nuitka because they feel that these things might not deliver everything CPython does, exactly like CPython does. Which is pretty terrible if you consider the heroic effort that the developer of Nuitka puts in to make his software work as similarly to CPython as possible, even going as far as to support Python 2 and Python 3, just as the PyPy team do.

Solutions like MicroPython have got away with certain incompatibilities with the justification that the target environment is rather constrained. But I imagine that even that project’s custodians get asked whether it can run Django, or whatever the arbitrarily-set threshold for technological validity might be. Never mind whether you would really want to run Django on a microcontroller or even on a phone. And never mind whether large parts of the mountain of code propping up such supposedly essential solutions could actually do with an audit and, in some cases, benefit from being retired and rewritten.

I am not fond of change for change’s sake, but new opportunities often bring new priorities and challenges with them. What then if Python as people insist on it today, with all the extra features added over the years to satisfy various petitioners and trends, is actually the weakness itself? What if the Python-like languages can adapt to these changes, and by having to confront their incompatibilities with hastily-written code from the 1990s and code employing “because it’s there” programming techniques, they can adapt to the changing environment while delivering much of what people like about Python in the first place? What if Python itself cannot?

“Why don’t you go and use something else if you don’t like what Python is?” some might ask. Certainly, Free Software itself is far more important to me than any adherence to Python. But I can also choose to make that other language something that carries forward the things I like about Python, not something that looks and behaves completely differently. And in doing so, at least I might gain a deeper understanding of what matters to me in Python, even if others refuse the lessons and the opportunities such Python-like languages can provide.

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