Support for variable length strings is only partially there. It may not be hard to add.

[bnlawrence]

If we attempt to read a variable length string created as follows:

_vlen_string = "foo"
dt = h5py.special_dtype(vlen=str)
v = ds.create_variable("var_len_str", ("x",), dtype=dt)
v[0] = _vlen_string

which would be read by h5py as v[0] and showing as dtype('O'), it shows
as dtype= ('VLEN_STRING', 0, 1) and an attempt to read v[0] returns:

NotImplementedError('datatype not implemented - {dtype_class}')