add helper to open returnn hdfs

lib/hdf.py

@@ -0,0 +1,24 @@
+import h5py
+import numpy as np
+from typing import Dict
+
+
+def get_input_dict_from_returnn_hdf(hdf_file: h5py.File) -> Dict[str, np.ndarray]:
+    """
+    Generate dictionary containing the "data" value as ndarray indexed by the sequence tag
+
+    :param hdf_file: HDF file to extract data from
+    :return:
+    """
+    inputs = hdf_file["inputs"]
+    seq_tags = hdf_file["seqTags"]
+    lengths = hdf_file["seqLengths"]
+
+    output_dict = {}
+    offset = 0
+    for tag, length in zip(seq_tags, lengths):
+        tag = tag if isinstance(tag, str) else tag.decode()
+        output_dict[tag] = inputs[offset : offset + length[0]]
+        offset += length[0]
+
+    return output_dict