Can h5py load a file from a byte array in memory?

You can use io.BytesIO or tempfile to create h5 objects, which showed in official docs http://docs.h5py.org/en/stable/high/file.html#python-file-like-objects.

The first argument to File may be a Python file-like object, such as an io.BytesIO or tempfile.TemporaryFile instance. This is a convenient way to create temporary HDF5 files, e.g. for testing or to send over the network.

tempfile.TemporaryFile

>>> tf = tempfile.TemporaryFile()
>>> f = h5py.File(tf)

or io.BytesIO

"""Create an HDF5 file in memory and retrieve the raw bytes

This could be used, for instance, in a server producing small HDF5
files on demand.
"""
import io
import h5py

bio = io.BytesIO()
with h5py.File(bio) as f:
    f['dataset'] = range(10)

data = bio.getvalue() # data is a regular Python bytes object.
print("Total size:", len(data))
print("First bytes:", data[:10])

You could try to use Binary I/O to create a File object and read it via h5py:

f = io.BytesIO(YOUR_H5PY_STREAM)
h = h5py.File(f,'r')