Merge pull request #160 from 2elli/3.10-fix-co_lines

Python 3.10 fix co_lines parsing of co_linetable

Author: rocky

xdis/codetype/code310.py

@@ -163,24 +163,32 @@ def co_lines(self):
                      either be a positive integer, or None
 
         Parsing implementation adapted from: https://github.com/python/cpython/blob/3.10/Objects/lnotab_notes.txt
+        The algorithm presented in the lnotab_notes.txt file is slightly inaccurate. The first linetable entry will have a line delta of 0, and should be yielded instead of skipped.
+        This implementation follows the lineiter definition in https://github.com/python/cpython/blob/3.10/Objects/codeobject.c#L1030.
         """
-        line = self.co_firstlineno
         end_offset = 0
+        line = self.co_firstlineno
+
         # co_linetable is pairs of (offset_delta: unsigned byte, line_delta: signed byte)
         for offset_delta, line_delta in struct.iter_unpack('=Bb', self.co_linetable):
             assert isinstance(line_delta, int)
             assert isinstance(offset_delta, int)
-            if line_delta == 0: # No change to line number, just accumulate changes to end
-                end_offset += offset_delta
-                continue
+            
             start_offset = end_offset
-            end_offset = start_offset + offset_delta
-            if line_delta == -128: # No valid line number -- skip entry
-                continue
-            line += line_delta
-            if end_offset == start_offset: # Empty range, omit.
+            end_offset += offset_delta
+            
+            # line_delta of -128 signifies an instruction range that is not associated with any line
+            if line_delta != -128:
+                line += line_delta
+                display_line = line
+            else:
+                display_line = None
+            
+            # omit empty ranges
+            if start_offset == end_offset:
                 continue
-            yield start_offset, end_offset, line
+
+            yield start_offset, end_offset, display_line
 
     def encode_lineno_tab(self):
         """