Fix numpy tostring warnings (#112)

Using the tostring function causes warnings like this starting in numpy 1.19:

  DeprecationWarning: tostring() is deprecated. Use tobytes() instead.

The simple fix is to replace them with tobytes which does the same thing.

nrrd/tests/test_writing.py

@@ -24,7 +24,7 @@ def write_and_read_back_with_encoding(self, encoding, level=9):
 
         # Read back the same file
         data, header = nrrd.read(output_filename, index_order=self.index_order)
-        self.assertEqual(self.expected_data, data.tostring(order=self.index_order))
+        self.assertEqual(self.expected_data, data.tobytes(order=self.index_order))
         self.assertEqual(header['encoding'], encoding)
 
         return output_filename
@@ -35,7 +35,7 @@ def test_write_default_header(self):
 
         # Read back the same file
         data, header = nrrd.read(output_filename, index_order=self.index_order)
-        self.assertEqual(self.expected_data, data.tostring(order=self.index_order))
+        self.assertEqual(self.expected_data, data.tobytes(order=self.index_order))
 
     def test_write_raw(self):
         self.write_and_read_back_with_encoding(u'raw')
@@ -170,7 +170,7 @@ def test_write_detached_raw_as_nrrd(self):
 
         # Read back the same file
         data, header = nrrd.read(output_filename, index_order=self.index_order)
-        self.assertEqual(self.expected_data, data.tostring(order=self.index_order))
+        self.assertEqual(self.expected_data, data.tobytes(order=self.index_order))
         self.assertEqual(header['encoding'], 'raw')
         self.assertEqual(header['data file'], output_data_filename)
 
@@ -182,7 +182,7 @@ def test_write_detached_raw_odd_extension(self):
 
         # Read back the same file
         data, header = nrrd.read(output_data_filename, index_order=self.index_order)
-        self.assertEqual(self.expected_data, data.tostring(order=self.index_order))
+        self.assertEqual(self.expected_data, data.tobytes(order=self.index_order))
         self.assertEqual(header['encoding'], 'raw')
         self.assertEqual('data file' in header, False)
 
@@ -202,7 +202,7 @@ def test_write_detached_raw(self):
 
         # Read back the same file
         data, header = nrrd.read(output_filename, index_order=self.index_order)
-        self.assertEqual(self.expected_data, data.tostring(order=self.index_order))
+        self.assertEqual(self.expected_data, data.tobytes(order=self.index_order))
         self.assertEqual(header['encoding'], 'raw')
         self.assertEqual(header['data file'], 'testfile_detached_raw.raw')
 
@@ -217,7 +217,7 @@ def test_write_detached_gz(self):
 
         # Read back the same file
         data, header = nrrd.read(output_filename, index_order=self.index_order)
-        self.assertEqual(self.expected_data, data.tostring(order=self.index_order))
+        self.assertEqual(self.expected_data, data.tobytes(order=self.index_order))
         self.assertEqual(header['encoding'], 'gz')
         self.assertEqual(header['data file'], output_data_filename)
 
@@ -231,7 +231,7 @@ def test_write_detached_bz2(self):
 
         # Read back the same file
         data, header = nrrd.read(output_filename, index_order=self.index_order)
-        self.assertEqual(self.expected_data, data.tostring(order=self.index_order))
+        self.assertEqual(self.expected_data, data.tobytes(order=self.index_order))
         self.assertEqual(header['encoding'], 'bz2')
         self.assertEqual(header['data file'], 'testfile_detached_raw.raw.bz2')
 
@@ -245,7 +245,7 @@ def test_write_detached_ascii(self):
 
         # Read back the same file
         data, header = nrrd.read(output_filename, index_order=self.index_order)
-        self.assertEqual(self.expected_data, data.tostring(order=self.index_order))
+        self.assertEqual(self.expected_data, data.tobytes(order=self.index_order))
         self.assertEqual(header['encoding'], 'txt')
         self.assertEqual(header['data file'], 'testfile_detached_raw.txt')
 

nrrd/writer.py

@@ -291,7 +291,7 @@ def _write_data(data, fh, header, compression_level=None, index_order='F'):
 
     if header['encoding'] == 'raw':
         # Convert the data into a string
-        raw_data = data.tostring(order=index_order)
+        raw_data = data.tobytes(order=index_order)
 
         # Write the data in chunks (see _WRITE_CHUNKSIZE declaration for more information why)
         # Obtain the length of the data since we will be using it repeatedly, more efficient
@@ -320,7 +320,7 @@ def _write_data(data, fh, header, compression_level=None, index_order='F'):
 
     else:
         # Convert the data into a string
-        raw_data = data.tostring(order=index_order)
+        raw_data = data.tobytes(order=index_order)
 
         # Construct the compressor object based on encoding
         if header['encoding'] in ['gzip', 'gz']: