[SPARK-21866][ML][PYTHON][FOLLOWUP] Few cleanups and fix image test failure in Python 3.6.0 / NumPy 1.13.3

## What changes were proposed in this pull request?

Image test seems failed in Python 3.6.0 / NumPy 1.13.3. I manually tested as below:

```
======================================================================
ERROR: test_read_images (pyspark.ml.tests.ImageReaderTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/.../spark/python/pyspark/ml/tests.py", line 1831, in test_read_images
    self.assertEqual(ImageSchema.toImage(array, origin=first_row[0]), first_row)
  File "/.../spark/python/pyspark/ml/image.py", line 149, in toImage
    data = bytearray(array.astype(dtype=np.uint8).ravel())
TypeError: only integer scalar arrays can be converted to a scalar index

----------------------------------------------------------------------
Ran 1 test in 7.606s
```

To be clear, I think the error seems from NumPy - 75b2d5d427/numpy/core/src/multiarray/number.c (L947)

For a smaller scope:

```python
>>> import numpy as np
>>> bytearray(np.array([1]).astype(dtype=np.uint8))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: only integer scalar arrays can be converted to a scalar index
```

In Python 2.7 / NumPy 1.13.1, it prints:

```
bytearray(b'\x01')
```

So, here, I simply worked around it by converting it to bytes as below:

```python
>>> bytearray(np.array([1]).astype(dtype=np.uint8).tobytes())
bytearray(b'\x01')
```

Also, while looking into it again, I realised few arguments could be quite confusing, for example, `Row` that needs some specific attributes and `numpy.ndarray`. I added few type checking and added some tests accordingly. So, it shows an error message as below:

```
TypeError: array argument should be numpy.ndarray; however, it got [<class 'str'>].
```

## How was this patch tested?

Manually tested with `./python/run-tests`.

And also:

```
PYSPARK_PYTHON=python3 SPARK_TESTING=1 bin/pyspark pyspark.ml.tests ImageReaderTest
```

Author: hyukjinkwon <gurwls223@gmail.com>

Closes #19835 from HyukjinKwon/SPARK-21866-followup.

python/pyspark/ml/image.py

@@ -108,12 +108,23 @@ class _ImageSchema(object):
         """
         Converts an image to an array with metadata.
 
-        :param image: The image to be converted.
+        :param `Row` image: A row that contains the image to be converted. It should
+            have the attributes specified in `ImageSchema.imageSchema`.
         :return: a `numpy.ndarray` that is an image.
 
         .. versionadded:: 2.3.0
         """
 
+        if not isinstance(image, Row):
+            raise TypeError(
+                "image argument should be pyspark.sql.types.Row; however, "
+                "it got [%s]." % type(image))
+
+        if any(not hasattr(image, f) for f in self.imageFields):
+            raise ValueError(
+                "image argument should have attributes specified in "
+                "ImageSchema.imageSchema [%s]." % ", ".join(self.imageFields))
+
         height = image.height
         width = image.width
         nChannels = image.nChannels
@@ -127,15 +138,20 @@ class _ImageSchema(object):
         """
         Converts an array with metadata to a two-dimensional image.
 
-        :param array array: The array to convert to image.
+        :param `numpy.ndarray` array: The array to convert to image.
         :param str origin: Path to the image, optional.
         :return: a :class:`Row` that is a two dimensional image.
 
         .. versionadded:: 2.3.0
         """
 
+        if not isinstance(array, np.ndarray):
+            raise TypeError(
+                "array argument should be numpy.ndarray; however, it got [%s]." % type(array))
+
         if array.ndim != 3:
             raise ValueError("Invalid array shape")
+
         height, width, nChannels = array.shape
         ocvTypes = ImageSchema.ocvTypes
         if nChannels == 1:
@@ -146,7 +162,12 @@ class _ImageSchema(object):
             mode = ocvTypes["CV_8UC4"]
         else:
             raise ValueError("Invalid number of channels")
-        data = bytearray(array.astype(dtype=np.uint8).ravel())
+
+        # Running `bytearray(numpy.array([1]))` fails in specific Python versions
+        # with a specific Numpy version, for example in Python 3.6.0 and NumPy 1.13.3.
+        # Here, it avoids it by converting it to bytes.
+        data = bytearray(array.astype(dtype=np.uint8).ravel().tobytes())
+
         # Creating new Row with _create_row(), because Row(name = value, ... )
         # orders fields by name, which conflicts with expected schema order
         # when the new DataFrame is created by UDF

python/pyspark/ml/tests.py

@@ -71,7 +71,7 @@ from pyspark.sql import DataFrame, Row, SparkSession
 from pyspark.sql.functions import rand
 from pyspark.sql.types import DoubleType, IntegerType
 from pyspark.storagelevel import *
-from pyspark.tests import ReusedPySparkTestCase as PySparkTestCase
+from pyspark.tests import QuietTest, ReusedPySparkTestCase as PySparkTestCase
 
 ser = PickleSerializer()
 
@@ -1836,6 +1836,24 @@ class ImageReaderTest(SparkSessionTestCase):
         self.assertEqual(ImageSchema.imageFields, expected)
         self.assertEqual(ImageSchema.undefinedImageType, "Undefined")
 
+        with QuietTest(self.sc):
+            self.assertRaisesRegexp(
+                TypeError,
+                "image argument should be pyspark.sql.types.Row; however",
+                lambda: ImageSchema.toNDArray("a"))
+
+        with QuietTest(self.sc):
+            self.assertRaisesRegexp(
+                ValueError,
+                "image argument should have attributes specified in",
+                lambda: ImageSchema.toNDArray(Row(a=1)))
+
+        with QuietTest(self.sc):
+            self.assertRaisesRegexp(
+                TypeError,
+                "array argument should be numpy.ndarray; however, it got",
+                lambda: ImageSchema.toImage("a"))
+
 
 class ALSTest(SparkSessionTestCase):