# pypy / pypy / doc / getting-started-python.rst

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# Getting Started with PyPy's Python Interpreter

PyPy's Python interpreter is a very compliant Python interpreter implemented in Python. When translated to C, it passes most of CPythons core language regression tests and comes with many of the extension modules included in the standard library including ctypes. It can run large libraries such as Django and Twisted. There are some small behavioral differences with CPython and some missing extensions, for details see CPython differences.

To actually use PyPy's Python interpreter, the first thing to do is to download a pre-built PyPy for your architecture.

## Translating the PyPy Python interpreter

(Note: for some hints on how to translate the Python interpreter under Windows, see the windows document)

You can translate the whole of PyPy's Python interpreter to low level C code, or CLI code.

1. First download a pre-built PyPy for your architecture which you will use to translate your Python interpreter. It is, of course, possible to translate with a CPython 2.6 or later, but this is not the preferred way, because it will take a lot longer to run -- depending on your architecture, between two and three times as long.

2. Install build-time dependencies. On a Debian box these are:

[user@debian-box ~]$sudo apt-get install \ gcc make python-dev libffi-dev pkg-config \ libz-dev libbz2-dev libncurses-dev libexpat1-dev \ libssl-dev libgc-dev python-sphinx python-greenlet  On a Fedora box these are: [user@fedora-or-rh-box ~]$ sudo yum install \
gcc make python-devel libffi-devel pkg-config \
zlib-devel bzip2-devel ncurses-devel expat-devel \
openssl-devel gc-devel python-sphinx python-greenlet


The above command lines are split with continuation characters, giving the necessary dependencies first, then the optional ones.

• pkg-config (to help us locate libffi files)
• libz-dev (for the optional zlib module)
• libbz2-dev (for the optional bz2 module)
• libncurses-dev (for the optional _minimal_curses module)
• libexpat1-dev (for the optional pyexpat module)
• libssl-dev (for the optional _ssl module)
• libgc-dev (for the Boehm garbage collector: only needed when translating with --opt=0, 1 or size)
• python-sphinx (for the optional documentation build. You need version 1.0.7 or later)
• python-greenlet (for the optional stackless support in interpreted mode/testing)
3. Translation is time-consuming -- 45 minutes on a very fast machine -- and RAM-hungry. As of March 2011, you will need at least 2 GB of memory on a 32-bit machine and 4GB on a 64-bit machine. If your memory resources are constrained, or your machine is slow you might want to pick the optimization level 1 in the next step. A level of 2 or 3 or jit gives much better results, though. But if all you want to do is to test that some new feature that you just wrote translates, level 1 is enough.

Let me stress this again: at --opt=1 you get the Boehm GC, which is here mostly for historical and for testing reasons. You really do not want to pick it for a program you intend to use. The resulting pypy-c is slow.

4. Run:

cd pypy/translator/goal
python translate.py --opt=jit targetpypystandalone.py


possibly replacing --opt=jit with another optimization level of your choice like --opt=2 if you do not want to include the JIT compiler, which makes the Python interpreter much slower.

If everything works correctly this will create an executable pypy-c in the current directory. Type pypy-c --help to see the options it supports - mainly the same basic options as CPython. In addition, pypy-c --info prints the translation options that where used to produce this particular executable. The executable behaves mostly like a normal Python interpreter:

$./pypy-c Python 2.7.0 (61ef2a11b56a, Mar 02 2011, 03:00:11) [PyPy 1.5.0-alpha0 with GCC 4.4.3] on linux2 Type "help", "copyright", "credits" or "license" for more information. And now for something completely different: this sentence is false'' >>>> 46 - 4 42 >>>> from test import pystone >>>> pystone.main() Pystone(1.1) time for 50000 passes = 0.280017 This machine benchmarks at 178561 pystones/second >>>>  This executable can be moved around or copied on other machines; see Installation below. The translate.py script takes a very large number of options controlling what to translate and how. See translate.py -h. Some of the more interesting options (but for now incompatible with the JIT) are: • --stackless: this produces a pypy-c that includes features inspired by Stackless Python. • --gc=boehm|ref|marknsweep|semispace|generation|hybrid|minimark: choose between using the Boehm-Demers-Weiser garbage collector, our reference counting implementation or one of own collector implementations (the default depends on the optimization level but is usually minimark). Find a more detailed description of the various options in our configuration sections. ### Translating with non-standard options It is possible to have non-standard features enabled for translation, but they are not really tested any more. Look, for example, at the objspace proxies document. ### Translating using the CLI backend To create a standalone .NET executable using the CLI backend: ./translate.py --backend=cli targetpypystandalone.py  The executable and all its dependencies will be stored in the ./pypy-cli-data directory. To run pypy.NET, you can run ./pypy-cli-data/main.exe. If you are using Linux or Mac, you can use the convenience ./pypy-cli script: $ ./pypy-cli
Python 2.7.0 (61ef2a11b56a, Mar 02 2011, 03:00:11)
[PyPy 1.5.0-alpha0] on linux2
Type "help", "copyright", "credits" or "license" for more information.
And now for something completely different: distopian and utopian chairs''
>>>>


Moreover, at the moment it's not possible to do the full translation using only the tools provided by the Microsoft .NET SDK, since ilasm crashes when trying to assemble the pypy-cli code due to its size. Microsoft .NET SDK 2.0.50727.42 is affected by this bug; other versions could be affected as well: if you find a version of the SDK that works, please tell us.

Windows users that want to compile their own pypy-cli can install Mono: if a Mono installation is detected the translation toolchain will automatically use its ilasm2 tool to assemble the executables.

To try out the experimental .NET integration, check the documentation of the clr module.

### Installation

A prebuilt pypy-c can be installed in a standard location like /usr/local/bin, although some details of this process are still in flux. It can also be copied to other machines as long as their system is "similar enough": some details of the system on which the translation occurred might be hard-coded in the executable.

For installation purposes, note that the executable needs to be able to find its version of the Python standard library in the following three directories: lib-python/2.7, lib-python/modified-2.7 and lib_pypy. They are located by "looking around" starting from the directory in which the executable resides. The current logic is to try to find a PREFIX from which the directories PREFIX/lib-python/2.7 and PREFIX/lib-python/modified.2.7 and PREFIX/lib_pypy can all be found. The prefixes that are tried are:

.
./lib/pypy1.5
..
../lib/pypy1.5
../..
../../lib/pypy-1.5
../../..
etc.


If the executable fails to find suitable libraries, it will report debug: WARNING: library path not found, using compiled-in sys.path and then attempt to continue normally. If the default path is usable, most code will be fine. However, the sys.prefix will be unset and some existing libraries assume that this is never the case.

## Running the Python Interpreter Without Translation

### The py.py interpreter

To start interpreting Python with PyPy, install a C compiler that is supported by distutils and use Python 2.5 or greater to run PyPy:

cd pypy
python bin/py.py


After a few seconds (remember: this is running on top of CPython), you should be at the PyPy prompt, which is the same as the Python prompt, but with an extra ">".

Now you are ready to start running Python code. Most Python modules should work if they don't involve CPython extension modules. This is slow, and most C modules are not present by default even if they are standard! Here is an example of determining PyPy's performance in pystones:

>>>> from test import pystone
>>>> pystone.main(10)


The parameter is the number of loops to run through the test. The default is 50000, which is far too many to run in a non-translated PyPy version (i.e. when PyPy's interpreter itself is being interpreted by CPython).

### py.py options

To list the PyPy interpreter command line options, type:

cd pypy
python bin/py.py --help


py.py supports most of the options that CPython supports too (in addition to a large amount of options that can be used to customize py.py). As an example of using PyPy from the command line, you could type:

python py.py -c "from test import pystone; pystone.main(10)"


Alternatively, as with regular Python, you can simply give a script name on the command line:

python py.py ../../lib-python/2.7/test/pystone.py 10


See our configuration sections for details about what all the commandline options do.