Welcome to PyOpenCL’s documentation!

PyOpenCL gives you easy, Pythonic access to the OpenCL parallel computation API. What makes PyOpenCL special?

  • Object cleanup tied to lifetime of objects. This idiom, often called RAII in C++, makes it much easier to write correct, leak- and crash-free code.
  • Completeness. PyOpenCL puts the full power of OpenCL’s API at your disposal, if you wish. Every obscure get_info() query and all CL calls are accessible.
  • Automatic Error Checking. All errors are automatically translated into Python exceptions.
  • Speed. PyOpenCL’s base layer is written in C++, so all the niceties above are virtually free.
  • Helpful Documentation. You’re looking at it. ;)
  • Liberal license. PyOpenCL is open-source under the MIT license and free for commercial, academic, and private use.

Here’s an example, to give you an impression:

import pyopencl as cl
import numpy
import numpy.linalg as la

a = numpy.random.rand(50000).astype(numpy.float32)
b = numpy.random.rand(50000).astype(numpy.float32)

ctx = cl.create_some_context()
queue = cl.CommandQueue(ctx)

mf = cl.mem_flags
a_buf = cl.Buffer(ctx, mf.READ_ONLY | mf.COPY_HOST_PTR, hostbuf=a)
b_buf = cl.Buffer(ctx, mf.READ_ONLY | mf.COPY_HOST_PTR, hostbuf=b)
dest_buf = cl.Buffer(ctx, mf.WRITE_ONLY, b.nbytes)

prg = cl.Program(ctx, """
    __kernel void sum(__global const float *a,
    __global const float *b, __global float *c)
      int gid = get_global_id(0);
      c[gid] = a[gid] + b[gid];

prg.sum(queue, a.shape, None, a_buf, b_buf, dest_buf)

a_plus_b = numpy.empty_like(a)
cl.enqueue_copy(queue, a_plus_b, dest_buf)

print(la.norm(a_plus_b - (a+b)), la.norm(a_plus_b))

(You can find this example as examples/demo.py in the PyOpenCL source distribution.)


Software that works with or enhances PyOpenCL

  • Bogdan Opanchuk’s reikna offers a variety of GPU-based algorithms (FFT, random number generation, matrix multiplication) designed to work with pyopencl.array.Array objects.
  • Gregor Thalhammer’s gpyfft provides a Python wrapper for the OpenCL FFT library clFFT from AMD.

If you know of a piece of software you feel that should be on this list, please let me know, or, even better, send a patch!

Indices and tables