AttributeError: 'Group' object has no attribute 'dtype' - dataset

Question

I want to combine the datasets within a single hdf5 file to form one dataset in a seperate file, but am struggling to set the dtype of the new dataset. I am getting the error AttributeError: 'Group' object has no attribute 'dtype' on the line with ds_0_dtype = h5f1[ds].dtype. the code below (based on some example code posted on stackoverflow)
with
h5py.File('xxx_xxx_signals.hdf5','r') as h5f1 , \
h5py.File('file2.h5','w') as h5f2 :
for i, ds in enumerate(h5f1.keys()) :
if i == 0:
ds_0 = ds
ds_0_dtype = h5f1[ds].dtype
n_rows = h5f1[ds].shape[0]
n_cols = h5f1[ds].shape[1]
else:
if h5f1[ds].dtype != ds_0_dtype :
print(f'Dset 0:{ds_0}: dtype:{ds_0_dtype}')
print(f'Dset {i}:{ds}: dtype:{h5f1[ds].dtype}')
sys.exit('Error: incompatible dataset dtypes')
if h5f1[ds].shape[0] != n_rows :
print(f'Dset 0:{ds_0}: shape[0]:{n_rows}')
print(f'Dset {i}:{ds}: shape[0]:{h5f1[ds].shape[0]}')
sys.exit('Error: incompatible dataset shape')
n_cols += h5f1[ds].shape[1]
prev_ds = ds
h5f2.create_dataset('ds_xxxx', dtype=ds_0_dtype, shape=(n_rows,n_cols), maxshape=(n_rows,None))
first = 0
for ds in h5f1.keys() :
xfer_arr = h5f1[ds][:]
last = first + xfer_arr.shape[1]
h5f2['ds_xxxx'][:, first:last] = xfer_arr[:]
first = last

Answer 1

Likely you have 1 or more Groups in addition to Datasets at the Root level. h5f1.keys() accesses all Nodes -- which can be Datasets or Groups. You need to add a test to skip over Groups. You do this with an isinstance() logic test. Something like this:
else:
if not isinstance(h5f1[ds], h5py.Dataset) :
print(f'Node 0:{ds_0}: is not a dataset')
sys.exit('Error: unexpected Group; only Datasets expected')
if h5f1[ds].dtype != ds_0_dtype :
Once you know how to identify groups, you can also modify code to avoid copying them to the second file. However, that may not be your desired result. I have an extended SO post on using isinstance(). See this link:
Is there a way to get datasets in all groups at once in h5py?