add example dump_dsets example (#226)

* add example

* fix flake8 errors

examples/dump_dsets.py

@@ -0,0 +1,79 @@
+import sys
+import h5py
+import h5pyd
+import s3fs
+from h5pyd import H5Image
+import numpy as np
+import time
+import logging
+
+CHUNKS_PER_PAGE = 8  # chunks_per_page for H5Image
+USE_CACHE = False    # use_cache setting for h5pyd.File
+
+
+def is_dataset(obj):
+    # this should work with either h5py or h5pyd
+    if obj.__class__.__name__ == "Dataset":
+        return True
+    else:
+        return False
+
+
+def visit(name, obj):
+    if not is_dataset(obj):
+        return
+    arr = obj[...]  # read entire dataset into numpy array
+    arr_mean = np.nan
+    arr_min = np.nan
+    arr_max = np.nan
+    try:
+        arr_mean = arr.mean()
+        arr_min = arr.min()
+        arr_max = arr.max()
+    except Exception:
+        # ignore errors on datasets that are not numeric
+        logging.warning(f"unable to use mean on {name}, dtype: {arr.dtype}")
+    print(f"{name:40} mean: {arr_mean:6.2f} min: {arr_min:0.2f} max: {arr_max:6.2f}")
+
+
+def main():
+
+    loglevel = logging.ERROR
+    logging.basicConfig(format='%(asctime)s %(message)s', level=loglevel)
+
+    if len(sys.argv) < 2 or sys.argv[1] in ("-h", "--help"):
+        print(f"usage: python {sys.argv[0]} <file_path>")
+        sys.exit(1)
+
+    filename = sys.argv[1]
+
+    start_time = time.time()
+
+    if filename.startswith("s3://"):
+        # use s3fs for access HDF5 files
+        s3 = s3fs.S3FileSystem(anon=True)
+        f = h5py.File(s3.open(filename, "rb"))
+    elif filename.startswith("hdf5://"):
+        # open HSDS domain
+        f = h5pyd.File(filename, use_cache=USE_CACHE)
+        if "h5image" in f:
+            # HDF5 file image, open with h5py and H5Image
+            f.close()
+            f = h5py.File(H5Image(filename, chunks_per_page=CHUNKS_PER_PAGE))
+    else:
+        # open HDF5 file
+        f = h5py.File(filename)
+
+    try:
+        f.visititems(visit)
+    except Exception as e:
+        logging.error(f"got exection {type(e)}: {e}")
+
+    f.close()
+
+    stop_time = time.time()
+    print("")
+    print(f"done - {(stop_time - start_time):4.3f} s")
+
+
+main()