"""
This example shows how to create and extend an unlimited dataset.
The program first writes integers to a dataset with dataspace
dimensions of DIM0xDIM1, then closes the file.  Next, it reopens
the file, reads back the data, outputs it to the screen, extends
the dataset, and writes new data to the entire extended dataset.
Finally it reopens the file again, reads back the data, and utputs
it to the screen.
"""
import numpy as np
import h5py

FILE = "h5ex_d_unlimmod.h5"
DATASET = "DS1"

DIM0 = 4
DIM1 = 7
EDIM0 = 6
EDIM1 = 10
CHUNK0 = 4
CHUNK1 = 4

def run():

    # Initialize the data.
    wdata = np.zeros((DIM0, DIM1), dtype=np.int32)
    for i in range(DIM0):
        for j in range(DIM1):
            wdata[i][j] = i * j - j

    with h5py.File(FILE, 'w') as f:
        dset = f.create_dataset(DATASET, (DIM0, DIM1), maxshape=(None, None),
                                chunks=(CHUNK0, CHUNK1), dtype='<i4')
        dset[...] = wdata

    # Now we begin the read section of this example.
    # Open the file and dataset.
    with h5py.File(FILE, 'r+') as f:
        dset = f[DATASET]

        rdata = dset[...]
        print("Dataset before extension:")
        print(rdata)

        dset.resize((EDIM0, EDIM1))

        # Initialize data for writing to the extended dataset.
        wdata = np.zeros((EDIM0, EDIM1), dtype=np.int32)
        for i in range(EDIM0):
            for j in range(EDIM1):
                wdata[i][j] = j

        # Write to the extended dataset.
        dset[...] = wdata

    # Now simply read back the data and echo to the screen.
    with h5py.File(FILE, 'r') as f:
        dset = f[DATASET]

        rdata = dset[...]
        print("Dataset after extension:")
        print(rdata)


if __name__ == "__main__":
    run()