Writing an HDF5 file containing a compound datatype

This is a bit more complex since it requires the implementation of a Python C-module that contains the datatype definition, and a couple of methods for converting data to a string and the other way around.

There is a small example located in the `hlhdf/pyhl' directory called `rave_info_type' which implements a small compound type definition. Basically this module defines an object containing xscale, yscale,xsize and ysize variables. This module has also got a type class which should be used.

import _pyhl
import _rave_info_type

# Create the rave info HDF5 type
typedef = _rave_info_type.type()

# Create the rave info HDF5 object
obj = _rave_info_type.object()

# Set the values
obj.xsize=10
obj.ysize=10
obj.xscale=150.0
obj.yscale=150.0

aList = _pyhl.nodelist()

# Create a datatype node
aNode = _pyhl.node(_pyhl.TYPE_ID,''/MyDatatype'')

# Make the datatype named
aNode.commit(typedef.hid())
aList.addNode(aNode)

# Create an attribute containing the compound type
aNode = _pyhl.node(_pyhl.ATTRIBUTE_ID,''/myCompoundAttribute'')

# Note that I use both itemSize and lhid
# Also note how I translate the compound object to a string
aNode.setScalarValue(typedef.size(),obj.tostring(),''compound'',typedef.hid())
aList.addNode(aNode)

# Better create a dataset also with the compound type
obj.xsize=1
obj.ysize=1
aNode = _pyhl.node(_pyhl.DATASET_ID,''/myCompoundDataset'')

# I use setArrayValue instead
aNode.setArrayValue(typedef.size(),[1],obj.tostring(),''compound'',typedef.hid())
aList.addNode(aNode)

# And finally write the HDF5 file.
aList.write(``compound_test.hdf'')

When checking this file with h5dump, the command syntax would be:

prompt% h5dump compound_test.hdf

And the result would be:

HDF5 "compound_test.hdf" {
GROUP "/" {
   ATTRIBUTE "myCompoundAttribute" {
      DATATYPE {
         H5T_STD_I32LE "xsize";
         H5T_STD_I32LE "ysize";
         H5T_IEEE_F64LE "xscale";
         H5T_IEEE_F64LE "yscale";
      }
      DATASPACE { SCALAR }
      DATA {
         {
            [ 10 ],
            [ 10 ],
            [ 150 ],
            [ 150 ]
         }
      }
   }
   DATATYPE "MyDatatype" {
      H5T_STD_I32LE "xsize";
      H5T_STD_I32LE "ysize";
      H5T_IEEE_F64LE "xscale";
      H5T_IEEE_F64LE "yscale";
   }
   DATASET "myCompoundDataset" {
      DATATYPE {
         "/MyDatatype"
      }
      DATASPACE { SIMPLE ( 1 ) / ( 1 ) }
      DATA {
         {
            [ 1 ],
            [ 1 ],
            [ 150 ],
            [ 150 ]
         }
      }
   }
}
}