Refactor string formatting to use f-strings (#128)

Python f-string's are the preferred approach to formatting strings and is supported since Python 3.6. Replace remaining old-style string-formatting to use f-string style.

Additionally, refactor certain error messages to be consistent with others.

nrrd/reader.py

@@ -143,7 +143,7 @@ def _parse_field_value(value, field_type):
         # for none rows. NaN is only valid for floating point numbers
         return parse_optional_matrix(value)
     else:
-        raise NRRDError('Invalid field type given: %s' % field_type)
+        raise NRRDError(f'Invalid field type given: {field_type}')
 
 
 def _determine_datatype(fields):
@@ -162,7 +162,7 @@ def _determine_datatype(fields):
         elif fields['endian'] == 'little':
             np_typestring = '<' + np_typestring
         else:
-            raise NRRDError('Invalid endian value in header: "%s"' % fields['endian'])
+            raise NRRDError(f'Invalid endian value in header: {fields["endian"]}')
 
     return np.dtype(np_typestring)
 
@@ -189,10 +189,10 @@ def _validate_magic_line(line):
     try:
         version = int(line[4:])
         if version > 5:
-            raise NRRDError('Unsupported NRRD file version (version: %i). This library only supports v%i and below.'
-                            % (version, 5))
+            raise NRRDError(f'Unsupported NRRD file version (version: {version}). This library only supports v5 '
+                            'and below.')
     except ValueError:
-        raise NRRDError('Invalid NRRD magic line: %s' % line)
+        raise NRRDError(f'Invalid NRRD magic line: {line}')
 
     return len(line)
 
@@ -279,12 +279,10 @@ def read_header(file, custom_field_map=None):
 
         # Check if the field has been added already
         if field in header.keys():
-            dup_message = "Duplicate header field: '%s'" % str(field)
-
             if not ALLOW_DUPLICATE_FIELD:
-                raise NRRDError(dup_message)
-
-            warnings.warn(dup_message)
+                raise NRRDError(f'Duplicate header field: {field}')
+            else:
+                warnings.warn(f'Duplicate header field: {field}')
 
         # Get the datatype of the field based on it's field name and custom field map
         field_type = _get_field_type(field, custom_field_map)
@@ -341,11 +339,11 @@ def read_data(header, fh=None, filename=None, index_order='F'):
     # Check that the required fields are in the header
     for field in _NRRD_REQUIRED_FIELDS:
         if field not in header:
-            raise NRRDError('Header is missing required field: "%s".' % field)
+            raise NRRDError(f'Header is missing required field: {field}')
 
     if header['dimension'] != len(header['sizes']):
-        raise NRRDError('Number of elements in sizes does not match dimension. Dimension: %i, len(sizes): %i' % (
-            header['dimension'], len(header['sizes'])))
+        raise NRRDError(f'Number of elements in sizes does not match dimension. Dimension: {header["dimension"]}, '
+                        f'len(sizes): {len(header["sizes"])}')
 
     # Determine the data type from the header
     dtype = _determine_datatype(header)
@@ -424,7 +422,7 @@ def read_data(header, fh=None, filename=None, index_order='F'):
             # to close it for us
             fh.close()
 
-            raise NRRDError('Unsupported encoding: "%s"' % header['encoding'])
+            raise NRRDError(f'Unsupported encoding: {header["encoding"]}')
 
         # Loop through the file and read a chunk at a time (see _READ_CHUNKSIZE why it is read in chunks)
         decompressed_data = bytearray()

nrrd/tests/test_reading.py

@@ -178,15 +178,15 @@ def test_read_dup_field_error_and_warn(self):
             expected_header = {'type': 'float', 'dimension': 3}
             header_txt_tuple = ('NRRD0005', 'type: float', 'dimension: 3', 'type: float')
 
-            with self.assertRaisesRegex(nrrd.NRRDError, "Duplicate header field: 'type'"):
+            with self.assertRaisesRegex(nrrd.NRRDError, "Duplicate header field: type"):
                 header = nrrd.read_header(header_txt_tuple)
 
             import warnings
             with warnings.catch_warnings(record=True) as w:
                 nrrd.reader.ALLOW_DUPLICATE_FIELD = True
                 header = nrrd.read_header(header_txt_tuple)
 
-                self.assertTrue("Duplicate header field: 'type'" in str(w[0].message))
+                self.assertTrue("Duplicate header field: type" in str(w[0].message))
 
                 self.assertEqual(expected_header, header)
                 nrrd.reader.ALLOW_DUPLICATE_FIELD = False
@@ -334,7 +334,7 @@ def test_missing_required_field(self):
                 # Delete required field
                 del header['type']
 
-                with self.assertRaisesRegex(nrrd.NRRDError, 'Header is missing required field: "type".'):
+                with self.assertRaisesRegex(nrrd.NRRDError, 'Header is missing required field: type'):
                     nrrd.read_data(header, fh, RAW_NRRD_FILE_PATH)
 
         def test_wrong_sizes(self):
@@ -357,7 +357,7 @@ def test_invalid_encoding(self):
                 # Set the encoding to be incorrect
                 header['encoding'] = 'fake'
 
-                with self.assertRaisesRegex(nrrd.NRRDError, 'Unsupported encoding: "fake"'):
+                with self.assertRaisesRegex(nrrd.NRRDError, 'Unsupported encoding: fake'):
                     nrrd.read_data(header, fh, RAW_NRRD_FILE_PATH)
 
         def test_detached_header_no_filename(self):
@@ -417,7 +417,7 @@ def test_invalid_endian(self):
                 # Set endianness to fake value
                 header['endian'] = 'fake'
 
-                with self.assertRaisesRegex(nrrd.NRRDError, 'Invalid endian value in header: "fake"'):
+                with self.assertRaisesRegex(nrrd.NRRDError, 'Invalid endian value in header: fake'):
                     nrrd.read_data(header, fh, RAW_NRRD_FILE_PATH)
 
         def test_invalid_index_order(self):

nrrd/tests/test_writing.py

@@ -303,7 +303,7 @@ def test_unsupported_encoding(self):
             output_filename = os.path.join(self.temp_write_dir, 'testfile_unsupported_encoding.nrrd')
             header = {'encoding': 'fake'}
 
-            with self.assertRaisesRegex(nrrd.NRRDError, 'Unsupported encoding: "fake"'):
+            with self.assertRaisesRegex(nrrd.NRRDError, 'Unsupported encoding: fake'):
                 nrrd.write(output_filename, np.zeros((3, 9)), header, index_order=self.index_order)
 
         def test_invalid_index_order(self):

nrrd/writer.py

@@ -93,7 +93,7 @@ def _format_field_value(value, field_type):
     elif field_type == 'double matrix':
         return format_optional_matrix(value)
     else:
-        raise NRRDError('Invalid field type given: %s' % field_type)
+        raise NRRDError(f'Invalid field type given: {field_type}')
 
 
 def _handle_header(data, header=None, index_order='F'):
@@ -220,7 +220,7 @@ def _write_data(data, fh, header, compression_level=None, index_order='F'):
         elif header['encoding'] in ['bzip2', 'bz2']:
             compressobj = bz2.BZ2Compressor(compression_level)
         else:
-            raise NRRDError('Unsupported encoding: "%s"' % header['encoding'])
+            raise NRRDError(f'Unsupported encoding: {header["encoding"]}')
 
         # 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
@@ -333,15 +333,15 @@ def write(file, data, header=None, detached_header=False, relative_data_path=Tru
             # Get the appropriate data filename based on encoding, see here for information on the standard detached
             # filename: http://teem.sourceforge.net/nrrd/format.html#encoding
             if header['encoding'] == 'raw':
-                data_filename = '%s.raw' % base_filename
+                data_filename = f'{base_filename}.raw'
             elif header['encoding'] in ['ASCII', 'ascii', 'text', 'txt']:
-                data_filename = '%s.txt' % base_filename
+                data_filename = f'{base_filename}.txt'
             elif header['encoding'] in ['gzip', 'gz']:
-                data_filename = '%s.raw.gz' % base_filename
+                data_filename = f'{base_filename}.raw.gz'
             elif header['encoding'] in ['bzip2', 'bz2']:
-                data_filename = '%s.raw.bz2' % base_filename
+                data_filename = f'{base_filename}.raw.bz2'
             else:
-                raise NRRDError('Invalid encoding specification while writing NRRD file: %s' % header['encoding'])
+                raise NRRDError(f'Invalid encoding specification while writing NRRD file: {header["encoding"]}')
 
         # Update the data file field in the header with the path of the detached data
         # TODO This will cause problems when the user specifies a relative data path and gives a custom path OUTSIDE
@@ -351,7 +351,7 @@ def write(file, data, header=None, detached_header=False, relative_data_path=Tru
         detached_header = True
     elif file.endswith('.nrrd') and detached_header:
         data_filename = file
-        file = '%s.nhdr' % os.path.splitext(file)[0]
+        file = f'{os.path.splitext(file)[0]}.nhdr'
         header['data file'] = os.path.basename(data_filename) \
             if relative_data_path else os.path.abspath(data_filename)
     else: