# Potential Project List

## Getting involved

We are happy to discuss ideas around the PyPy ecosystem. If you are interested in playing with RPython or PyPy, or have a new idea not mentioned here please join us on irc, channel #pypy (irc.libera.chat). If you are unsure, but still think that you can make a valuable contribution to PyPy, dont hesitate to contact us on #pypy or on our mailing list. Here are some ideas to get you thinking:

- Optimize PyPy Memory Usage: Sometimes PyPy consumes more memory than CPython. Two examples: 1) PyPy seems to allocate and keep alive more strings when importing a big Python modules. 2) The base interpreter size (cold VM started from a console) of PyPy is bigger than the one of CPython. The general procedure of this project is: Run both CPython and PyPy of the same Python version and compare the memory usage (using Massif or other tools). If PyPy consumes a lot more memory then find and resolve the issue.

- VMProf + memory profiler: vmprof is a statistical memory profiler. We want extend it with new features and resolve some current limitations.

- VMProf visualisations: vmprof shows a flame graph of the statistical profile and some more information about specific call sites. It would be very interesting to experiment with different information (such as memory, or even information generated by our jit compiler).

- Explicit typing in RPython: PyPy wants to have better ways to specify the signature and class attribute types in RPython. See more information about this topic below on this page.

- Virtual Reality (VR) visualisations for vmprof: This is a very open topic with lots of freedom to explore data visualisation for profiles. No VR hardware would be needed for this project. Either universities provide such hardware or in any other case we potentially can lend the VR hardware setup.

## Simple tasks for newcomers

- Optimize random: https://github.com/pypy/pypy/issues/1901

- Implement AF_XXX packet types of sockets: https://github.com/pypy/pypy/issues/1942

- Help with documentation. One task would be to document rpython configuration options currently listed only on this site also on the RPython documentation site.

## Mid-to-large tasks

Below is a list of projects that are interesting for potential contributors who are seriously interested in the PyPy project. They mostly share common patterns - they're mid-to-large in size, they're usually well defined as a standalone projects and they're not being actively worked on. For small projects that you might want to work on look above or either look at the issue tracker, pop up on #pypy on irc.libera.chat or write to the mailing list. This is simply for the reason that small possible projects tend to change very rapidly.

This list is mostly for having an overview on potential projects. This list is by definition not exhaustive and we're pleased if people come up with their own improvement ideas. In any case, if you feel like working on some of those projects, or anything else in PyPy, pop up on IRC or write to us on the mailing list.

## Explicit typing in RPython

RPython is mostly based around type inference, but there are many cases where specifying types explicitly is useful. We would like to be able to optionally specify the exact types of the arguments to any function. We already have solutions in that space, `@rpython.rlib.objectmodel.enforceargs` and `@rpython.rlib.signature.signature`, but they are inconvenient and limited. For instance, they do not easily allow to express the type "dict with ints as keys and lists of instances of Foo as values".

Additionally, we would like to be able to specify the types of instance attributes. Unlike the function case, this is likely to require some refactoring of the annotator.

## Make bytearray type fast

PyPy's bytearray type is very inefficient. It would be an interesting task to look into possible optimizations on this. (XXX current status unknown; ask on #pypy for updates on this.)

## Implement copy-on-write list slicing

The idea is to have a special implementation of list objects which is used when doing `myslice = mylist[a:b]`: the new list is not constructed immediately, but only when (and if) `myslice` or `mylist` are mutated.

## NumPy rebooted

Our cpyext C-API compatiblity layer can now run upstream NumPy unmodified. We need to refactor the way NumPy adds docstrings.

We also are looking for help in how to hijack NumPy dtype conversion and ufunc calls to allow the JIT to make them fast, using our internal _numpypy module.

## Improving the jitviewer

Analyzing performance of applications is always tricky. We have various tools, for example a jitviewer that help us analyze performance.

The old tool was partly rewritten and combined with vmprof. The service is hosted at vmprof.com.

The following shows an old image of the jitviewer. The code generated by the PyPy JIT in a hierarchical way:

> - at the bottom level, it shows the Python source code of the compiled loops

> - for each source code line, it shows the corresponding Python bytecode

> - for each opcode, it shows the corresponding jit operations, which are the ones actually sent to the backend for compiling (such as `i15 = i10 < 2000` in the example)

The jitviewer is a web application based on django and angularjs: if you have great web developing skills and want to help PyPy, this is an ideal task to get started, because it does not require any deep knowledge of the internals. Head over to vmprof-python, vmprof-server and vmprof-integration to find open issues and documentation.

## Convert RPython to Python3

The world is moving on, we should too. Work in this direction has begun on the `rpython3` branch, mainly to enable building documentation with Python3. Some things that are known to need careful refactoring:

- a single character in python3 is an int, not a byte

- we use `str`/`unicode` to distiguish between different modes of operation for windows in `make_win32_traits`.

There are probably more. The branch currently does not pass rpython tests so work is needed to back out some of the changes and redo them properly

## Improve performance

- Make uninlined Python-level calls faster

- Switch to a sea-of-nodes IR, or a Lua-Jit-like IR which iterates on on the sea-of-nodes approach

- Use real register-allocation

- Improve instruction selection / scheduling

- Create a hybrid tracing/method JIT

## Improve warmup

- Interpreter speed-ups

- Optimize while tracing

- Cache information between runs

## Translation Toolchain

(XXX this is unlikely to be feasible.)

- Incremental or distributed translation.

- Allow separate compilation of extension modules.

## Various GCs

PyPy has pluggable garbage collection policy. This means that various garbage collectors can be written for specialized purposes, or even various experiments can be done for the general purpose. Examples:

- A garbage collector that compact memory better for mobile devices

- A concurrent garbage collector (a lot of work)

- A collector that keeps object flags in separate memory pages, to avoid un-sharing all pages between several fork()ed processes

## STM (Software Transactional Memory)

This was an experiment that we stopped developing. Besides the main development path, whose goal is to make a (relatively fast) version of pypy which includes STM, there are independent topics that can already be experimented with on the existing, JIT-less pypy-stm version:

- What kind of conflicts do we get in real use cases? And, sometimes, which data structures would be more appropriate? For example, a dict implemented as a hash table will suffer "stm collisions" in all threads whenever one thread writes anything to it; but there could be other implementations. Maybe alternate strategies can be implemented at the level of the Python interpreter (see list/dict strategies, `pypy/objspace/std/{list,dict}object.py`).

- More generally, there is the idea that we would need some kind of "debugger"-like tool to "debug" things that are not bugs, but stm conflicts. How would this tool look like to the end Python programmers? Like a profiler? Or like a debugger with breakpoints on aborted transactions? It would probably be all app-level, with a few hooks e.g. for transaction conflicts.

- Find good ways to have libraries using internally threads and atomics, but not exposing threads to the user. Right now there is a rough draft in `lib_pypy/transaction.py`, but much better is possible. For example we could probably have an iterator-like concept that allows each loop iteration to run in parallel.

## Introduce new benchmarks

Our benchmark runner is showing its age. We should merge with the CPython site

Additionally, we're usually happy to introduce new benchmarks. Please consult us before, but in general something that's real-world python code and is not already represented is welcome. We need at least a standalone script that can run without parameters. Example ideas (benchmarks need to be got from them!):

- hg

## Interfacing with C

While we could make `cpyext` faster, we would also like to explore other ideas. While cffi is appropriate for small to medium-sized extensions, HPy seems to be the way forward for Python C-extensions. Here are a few ideas: * Help HPy and port projects to it * Extend Cython to have a backend that can be understood by the JIT * Collaborate with C-extension authors to ensure full PyPy support (see below) * Put PyPy compatible packages on PyPI and in conda

### Make more python modules pypy-friendly

A lot of work has gone into PyPy's implementation of CPython's C-API, cpyext, over the last years to let it reach a practical level of compatibility, so that C extensions for CPython work on PyPy without major rewrites. However, there are still many edges and corner cases where it misbehaves.

For any popular extension that does not already advertise full PyPy compatibility, it would thus be useful to take a close look at it in order to make it fully compatible with PyPy. The general process is something like:

- Run the extension's tests on PyPy and look at the test failures.

- Some of the failures may be solved by identifying cases where the extension relies on undocumented or internal details of CPython, and rewriting the relevant code to follow documented best practices. Open issues and send pull requests as appropriate given the extension's development process.

- Other failures may highlight incompatibilities between cpyext and CPython. Please report them to us and try to fix them.

- Run benchmarks, either provided by the extension developers or created by you. Any case where PyPy is significantly slower than CPython is to be considered a bug and solved as above.

Alternatively, an approach we used to recommend was to rewrite C extensions using more pypy-friendly technologies, e.g. cffi. Here is a partial list of good work that needs to be finished:

wxPython-cffi archived copy of the bitbucket repo

> Status: A project by a PyPy developer to adapt the Phoenix sip build system to cffi

> The project is a continuation of a 2013 GSOC https://waedt.blogspot.com/

> TODO: Revive the archive, merge the latest version of the wrappers and finish the sip conversion

pygame https://github.com/CTPUG/pygame_cffi

> Status: Last release was in 2017