helper fn to download mnist from public s3

Author: Hongshan Li

utils/datasets.py

@@ -0,0 +1,34 @@
+import boto3
+
+PUBLIC_BUCKET = "sagemaker-sample-files"
+
+def download_mnist(data_dir='/tmp/data', train=True):
+    """Download MNIST dataset from a public S3 bucket
+    
+    Args:
+        data_dir (str): directory to save the data
+        train (bool): download training set
+    
+    Returns:
+        None
+    """
+    
+    if not os.path.exists(data_dir):
+        os.makedirs(data_dir)
+    
+    if train:
+        images_file = "train-images-idx3-ubyte.gz"
+        labels_file = "train-labels-idx1-ubyte.gz"
+    else:
+        images_file = "t10k-images-idx3-ubyte.gz"
+        labels_file = "t10k-labels-idx1-ubyte.gz"
+
+    # download objects
+    s3 = boto3.client('s3')
+    for obj in [images_file, labels_file]:
+        key = os.path.join("datasets/image/MNIST", obj)
+        dest = os.path.join(data_dir, obj)
+        if not os.path.exists(dest):
+            s3.download_file(PUBLIC_BUCKET, key, dest)
+    return 
+