how to write data to a h5py dataset

Question

I'm going crazy here - for some reason, I can't find out how to change a dataset in h5py. I first create a file:

i = h.File('C:\\Users\Bob\Desktop\blob.h5','w')

I then create a dataset within the file:

i.create_dataset("data",(100,100,100))

Finally, I try to write to the dataset:

i['data'][0][0][0] = 5

However, when I print, I don't get 5 back!

print(i['data'][0][0][0])#returns 0

I tried closing and reopening the file, but that didn't help. Any suggestions would be greatly appreciated!

Answer 1

So far, I haven't been able to find a way to mutate the contents of a dataset, but here's how to successfully create a new dataset. First, store the data in a list (this could be a multi-dimensional numpy array instead):

l = [1,2,3]

Then, create the dataset:

i.create_dataset("array", data=l) 
arr = i["array"]

print(arr[1]) will now correctly display the value 2

Answer 2

Change the file mode argument for h5py.File from w to r+ for read/write or a for read/write/create. See https://docs.h5py.org/en/stable/high/file.html