add Exception subclasses and basic logging

mnists/__init__.py

@@ -10,6 +10,7 @@ __version__ = "0.2.1"
 import array
 import gzip
 import hashlib
+import logging
 import numpy as np
 import os
 import os.path
@@ -18,17 +19,16 @@ import sys
 from urllib.request import urlretrieve
 
 from .hashes import hashes
+from .exceptions import *
 
 
+logger = logging.getLogger(__name__)
+
 home = os.path.expanduser("~")
 output_directory = os.path.join(home, ".mnist")
 webhost = "https://eaguru.guru/mnist/"
 
 
-def lament(*args, **kwargs):
-    print(*args, file=sys.stderr, **kwargs)
-
-
 def make_meta(npz, train_part="train", test_part="t10k", prefix=""):
     images_suffix = "-images-idx3-ubyte.gz"
     labels_suffix = "-labels-idx1-ubyte.gz"
@@ -68,6 +68,7 @@ def make_directories():
     directories += [construct_path(meta[0]) for meta in metadata.values()]
     for directory in directories:
         if not os.path.isdir(directory):
+            logger.info("Creating directory %s", directory)
             os.mkdir(directory)
 
 
@@ -75,19 +76,21 @@ def download(name):
     url_name = "/".join(os.path.split(name))
     path = construct_path(name)
     already_exists = os.path.isfile(path)
-    if not already_exists:
+    if already_exists:
+        logger.debug("Not downloading %s, it already exists: %s", name, path)
+    else:
         url = webhost + url_name
         try:
             urlretrieve(url, path)
         except Exception:
-            lament(f"Failed to download {url} to {path}")
+            logger.warning("Failed to download %s to %s", url, path)
             raise
     return already_exists
 
 
 def validate(name):
     if name not in hashes.keys():
-        raise Exception(f"Unknown mnist dataset: {name}")
+        raise UnknownDatasetError(name)
 
     with open(construct_path(name), "rb") as f:
         data = f.read()
@@ -96,9 +99,7 @@ def validate(name):
     hash = hashlib.sha256(data).hexdigest()
 
     if hash != known_hash:
-        raise Exception(f"""Failed to validate dataset: {name}
+        raise IntegrityError(file, known_hash, hash)
-Hash mismatch: {hash} should be {known_hash}
-Please check your local file for tampering or corruption.""")
 
 
 def onehot(ind):
@@ -113,9 +114,13 @@ def read_array(f):
     return np.array(array.array("B", f.read()), dtype=np.uint8)
 
 
-def open_maybe_gzip(path):
+def open_maybe_gzip(path, flags="rb"):
-    opener = gzip.open if path.endswith(".gz") else open
+    if path.endswith(".gz"):
-    return opener(path, "rb")
+        logger.debug("Opening %s with gzip.open", path)
+        return gzip.open(path, flags)
+    else:
+        logger.debug("Opening %s with builtin open", path)
+        return open(path, flags)
 
 
 def load(images_path, labels_path):
@@ -150,7 +155,7 @@ def batch_flatten(x):
 def prepare(dataset="mnist", return_floats=True, return_onehot=True,
             flatten=False, squeeze_labels=True, check_integrity=True):
     if dataset not in metadata.keys():
-        raise Exception(f"Unknown dataset: {dataset}")
+        raise UnknownDatasetError(dataset)
 
     meta = metadata[dataset]
     prefix, names = meta[0], meta[1:]
@@ -158,6 +163,9 @@ def prepare(dataset="mnist", return_floats=True, return_onehot=True,
     npz, train_images, train_labels, test_images, test_labels = names
     images_and_labels = names[1:]
 
+    logger.debug("Filenames chosen for %s: %s, %s, %s, %s",
+                 dataset, train_images, train_labels, test_images, test_labels)
+
     make_directories()
 
     existing = [os.path.isfile(construct_path(name)) for name in names]
@@ -169,6 +177,7 @@ def prepare(dataset="mnist", return_floats=True, return_onehot=True,
             validate(name)
 
     if npz_existing:
+        logger.info("Loading npz file %s", npz)
         with np.load(construct_path(npz)):
             train_images_data, train_labels_data, \
                 test_images_data, test_labels_data = \

mnists/__main__.py

@@ -1,5 +1,10 @@
-from . import metadata, prepare
+import logging
 
+from . import metadata, prepare, logger
+
+
+logging.basicConfig()
+logger.setLevel(logging.DEBUG)
 
 headers = ("subdirectory",
            "dataset",

mnists/exceptions.py

@@ -0,0 +1,18 @@
+class IntegrityError(Exception):
+    def __init__(self, file, expected_hash, computed_hash):
+        self.file = file
+        self.expected_hash = expected_hash
+        self.computed_hash = computed_hash
+
+    def __str__(self):
+        return f"""Failed to validate dataset: {name}
+Hash mismatch: {self.computed_hash} should be {self.expected_hash}
+Please check your local file for tampering or corruption."""
+
+
+class UnknownDatasetError(Exception):
+    def __init__(self, dataset):
+        self.dataset = dataset
+
+    def __str__(self):
+        return f"Unknown mnist-like dataset: {dataset}"