Edit: I changed the program to illustrate the char4 usage instead of float4:
import numpy as np
import pyopencl as cl
import pyopencl.array as cl_array
deviceID = 0
platformID = 0
workGroup=(1,1)
N = 10
testData = np.zeros(N, dtype=cl_array.vec.char4)
dev = cl.get_platforms()[platformID].get_devices()[deviceID]
ctx = cl.Context([dev])
queue = cl.CommandQueue(ctx)
mf = cl.mem_flags
Data_In = cl.Buffer(ctx, mf.READ_WRITE, testData.nbytes)
prg = cl.Program(ctx, """
__kernel void Pack_Cmplx( __global char4* Data_In, int N)
{
int gid = get_global_id(0);
//Data_In[gid] = 1; // This would change all components to one
Data_In[gid].x = 1; // changing single component
Data_In[gid].y = 2;
Data_In[gid].z = 3;
Data_In[gid].w = 4;
}
""").build()
prg.Pack_Cmplx(queue, (N,1), workGroup, Data_In, np.int32(N))
cl.enqueue_copy(queue, testData, Data_In)
print testData
I hope it helps.