add a check that filename passed to nd2reader has an extension .nd2 because...

add a check that filename passed to nd2reader has an extension .nd2 because the current implementation raises InvalidVersionError if the passed file is non-nd2 type, which is misleading

add an exception InvalidFileType

add a test for the new behavior of ND2Reader constructor

nd2reader/exceptions.py

+class InvalidFileType(Exception):
+    """Non .nd2 extension file.
+
+    File does not have an extension .nd2.
+
+    """
+    pass
+
 class InvalidVersionError(Exception):
     """Unknown version.
 

nd2reader/reader.py

 from pims import Frame
 from pims.base_frames import FramesSequenceND
 
-from nd2reader.exceptions import EmptyFileError
+from nd2reader.exceptions import EmptyFileError, InvalidFileType
 from nd2reader.parser import Parser
 import numpy as np
 
@@ -15,6 +15,10 @@ class ND2Reader(FramesSequenceND):
 
     def __init__(self, filename):
         super(ND2Reader, self).__init__()
+
+        if not filename.endswith(".nd2"):
+            raise InvalidFileType(f"The file {filename} you want to read with nd2reader does not have extension .nd2.")
+
         self.filename = filename
 
         # first use the parser to parse the file

tests/test_reader.py

@@ -4,12 +4,15 @@ import struct
 
 from pims import Frame
 from nd2reader.artificial import ArtificialND2
-from nd2reader.exceptions import EmptyFileError
+from nd2reader.exceptions import EmptyFileError, InvalidFileType
 from nd2reader.reader import ND2Reader
 from nd2reader.parser import Parser
 
 
 class TestReader(unittest.TestCase):
+    def test_invalid_file_extension(self):
+        self.assertRaises(InvalidFileType, lambda: ND2Reader('test_data/invalid_extension_file.inv'))
+
     def test_extension(self):
         self.assertTrue('nd2' in ND2Reader.class_exts())