pypy / pypy / doc / getting-started-dev.rst

Getting Started with the Translation Toolchain and Development Process

Trying out the translator

The translator is a tool based on the PyPy interpreter which can translate sufficiently static RPython programs into low-level code (in particular it can be used to translate the full Python interpreter). To be able to experiment with it you need to:

To start the interactive translator shell do:

cd pypy
python bin/translatorshell.py

Test snippets of translatable code are provided in the file pypy/translator/test/snippet.py, which is imported under the name snippet. For example:

>>> t = Translation(snippet.is_perfect_number, [int])
>>> t.view()

After that, the graph viewer pops up, that lets you interactively inspect the flow graph. To move around, click on something that you want to inspect. To get help about how to use it, press 'H'. To close it again, press 'Q'.

Trying out the type annotator

We have a type annotator that can completely infer types for functions like is_perfect_number (as well as for much larger examples):

>>> t.annotate()
>>> t.view()

Move the mouse over variable names (in red) to see their inferred types.

Translating the flow graph to C code

The graph can be turned into C code:

>>> t.rtype()
>>> f = t.compile_c()

The first command replaces the operations with other low level versions that only use low level types that are available in C (e.g. int). To try out the compiled version:

>>> f(5)
False
>>> f(6)
True

Translating the flow graph to CLI or JVM code

PyPy also contains a CLI backend and JVM backend which can translate flow graphs into .NET executables or a JVM jar file respectively. Both are able to translate the entire interpreter. You can try out the CLI and JVM backends from the interactive translator shells as follows:

>>> def myfunc(a, b): return a+b
...
>>> t = Translation(myfunc, [int, int])
>>> t.annotate()
>>> f = t.compile_cli() # or compile_jvm()
>>> f(4, 5)
9

The object returned by compile_cli or compile_jvm is a wrapper around the real executable: the parameters are passed as command line arguments, and the returned value is read from the standard output.

Once you have compiled the snippet, you can also try to launch the executable directly from the shell. You will find the executable in one of the /tmp/usession-* directories:

# For CLI:
$ mono /tmp/usession-trunk-<username>/main.exe 4 5
9

# For JVM:
$ java -cp /tmp/usession-trunk-<username>/pypy pypy.Main 4 5
9

To translate and run for the CLI you must have the SDK installed: Windows users need the .NET Framework SDK, while Linux and Mac users can use Mono. To translate and run for the JVM you must have a JDK installed (at least version 6) and java/javac on your path.

A slightly larger example

There is a small-to-medium demo showing the translator and the annotator:

cd demo
../pypy/translator/goal/translate.py --view --annotate bpnn.py

This causes bpnn.py to display itself as a call graph and class hierarchy. Clicking on functions shows the flow graph of the particular function. Clicking on a class shows the attributes of its instances. All this information (call graph, local variables' types, attributes of instances) is computed by the annotator.

To turn this example to C code (compiled to the executable bpnn-c), type simply:

../pypy/translator/goal/translate.py bpnn.py

Translating Full Programs

To translate full RPython programs, there is the script translate.py in translator/goal. Examples for this are a slightly changed version of Pystone:

cd pypy/translator/goal
python translate.py targetrpystonedalone

This will produce the executable "targetrpystonedalone-c".

The largest example of this process is to translate the full Python interpreter. There is also an FAQ about how to set up this process for your own interpreters.

Where to start reading the sources

PyPy is made from parts that are relatively independent of each other. You should start looking at the part that attracts you most (all paths are relative to the PyPy top level directory). You may look at our directory reference or start off at one of the following points:

Running PyPy's unit tests

PyPy development always was and is still thoroughly test-driven. We use the flexible py.test testing tool which you can install independently and use for other projects.

The PyPy source tree comes with an inlined version of py.test which you can invoke by typing:

python pytest.py -h

This is usually equivalent to using an installed version:

py.test -h

If you encounter problems with the installed version make sure you have the correct version installed which you can find out with the --version switch.

Now on to running some tests. PyPy has many different test directories and you can use shell completion to point at directories or files:

py.test pypy/interpreter/test/test_pyframe.py

# or for running tests of a whole subdirectory
py.test pypy/interpreter/

See py.test usage and invocations for some more generic info on how you can run tests.

Beware trying to run "all" pypy tests by pointing to the root directory or even the top level subdirectory pypy. It takes hours and uses huge amounts of RAM and is not recommended.

To run CPython regression tests you can point to the lib-python directory:

py.test lib-python/2.7/test/test_datetime.py

This will usually take a long time because this will run the PyPy Python interpreter on top of CPython. On the plus side, it's usually still faster than doing a full translation and running the regression test with the translated PyPy Python interpreter.

Special Introspection Features of the Untranslated Python Interpreter

If you are interested in the inner workings of the PyPy Python interpreter, there are some features of the untranslated Python interpreter that allow you to introspect its internals.

Interpreter-level console

If you start an untranslated Python interpreter via:

python pypy/bin/pyinteractive.py

If you press <Ctrl-C> on the console you enter the interpreter-level console, a usual CPython console. You can then access internal objects of PyPy (e.g. the object space) and any variables you have created on the PyPy prompt with the prefix w_:

>>>> a = 123
>>>> <Ctrl-C>
*** Entering interpreter-level console ***
>>> w_a
W_IntObject(123)

The mechanism works in both directions. If you define a variable with the w_ prefix on the interpreter-level, you will see it on the app-level:

>>> w_l = space.newlist([space.wrap(1), space.wrap("abc")])
>>> <Ctrl-D>
*** Leaving interpreter-level console ***

KeyboardInterrupt
>>>> l
[1, 'abc']

Note that the prompt of the interpreter-level console is only '>>>' since it runs on CPython level. If you want to return to PyPy, press <Ctrl-D> (under Linux) or <Ctrl-Z>, <Enter> (under Windows).

You may be interested in reading more about the distinction between interpreter-level and app-level.

Tracing bytecode and operations on objects

You can use the trace object space to monitor the interpretation of bytecodes in connection with object space operations. To enable it, set __pytrace__=1 on the interactive PyPy console:

>>>> __pytrace__ = 1
Tracing enabled
>>>> a = 1 + 2
|- <<<< enter <inline>a = 1 + 2 @ 1 >>>>
|- 0    LOAD_CONST    0 (W_IntObject(1))
|- 3    LOAD_CONST    1 (W_IntObject(2))
|- 6    BINARY_ADD
  |-    add(W_IntObject(1), W_IntObject(2))   -> W_IntObject(3)
|- 7    STORE_NAME    0 (a)
  |-    hash(W_StringObject('a'))   -> W_IntObject(-468864544)
  |-    int_w(W_IntObject(-468864544))   -> -468864544
|-10    LOAD_CONST    2 (<W_NoneObject()>)
|-13    RETURN_VALUE
|- <<<< leave <inline>a = 1 + 2 @ 1 >>>>

Demos

The `demo/`_ directory contains examples of various aspects of PyPy, ranging from running regular Python programs (that we used as compliance goals) over experimental distribution mechanisms to examples translating sufficiently static programs into low level code.

Additional Tools for running (and hacking) PyPy

We use some optional tools for developing PyPy. They are not required to run the basic tests or to get an interactive PyPy prompt but they help to understand and debug PyPy especially for the translation process.

py.test and the py lib

The py.test testing tool drives all our testing needs.

We use the py library for filesystem path manipulations, terminal writing, logging and some other support functionality.

You don't necessarily need to install these two libraries because we also ship them inlined in the PyPy source tree.

Getting involved

PyPy employs an open development process. You are invited to join our pypy-dev mailing list or look at the other contact possibilities. Usually we give out commit rights fairly liberally, so if you want to do something with PyPy, you can become a committer. We are also doing coding Sprints which are separately announced and often happen around Python conferences such as EuroPython or Pycon. Upcoming events are usually announced on the blog.

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