deduperreload gives invalid tracebacks in reloaded functions

When a function is reloaded with deduperreload, the line number information from the source file is lost. This breaks tracebacks, causing them to point to the start of the file instead of the correct source line. The reported line number matches the offset from the start of the function (plus one if the function is inside a class), but any comments and blank lines are ignored.

Tested with Python 3.13.14, IPython 9.15.0.

Python 3.13.14 | packaged by conda-forge | (main, Jun 12 2026, 09:50:25) [GCC 14.3.0]
Type 'copyright', 'credits' or 'license' for more information
IPython 9.15.0 -- An enhanced Interactive Python. Type '?' for help.

In [1]: %load_ext autoreload

In [2]: %autoreload -p 1

In [3]: %%writefile module.py
   ...: """
   ...: The traceback incorrectly points to this line (line 2 of the file)
   ...: """
   ...: def func():
   ...:     assert False, "before reload"
   ...:
   ...:

In [4]: %aimport module

In [5]: module.func()
---------------------------------------------------------------------------
AssertionError                            Traceback (most recent call last)
Cell In[5], line 1
----> 1 module.func()

File /tmp/module.py:5, in func()
      4 def func():
----> 5     assert False, "before reload"

AssertionError: before reload

In [6]: %%writefile module.py
   ...: """
   ...: The traceback incorrectly points to this line (line 2 of the file)
   ...: """
   ...: def func():
   ...:     assert False, "after reload"
   ...:
   ...:
Overwriting module.py

In [7]: module.func()
Reloading 'module'.
---------------------------------------------------------------------------
AssertionError                            Traceback (most recent call last)
Cell In[7], line 1
----> 1 module.func()

File /tmp/module.py:2, in func()
      1 """
----> 2 The traceback incorrectly points to this line (line 2 of the file)
      3 """
      4 def func():
      5     assert False, "after reload"

AssertionError: after reload

I'm not sure why DeduperReloader._patch_namespace_inner() unparses the AST node to text here instead of directly wrapping it with an ast.ClassDef:

ipython/IPython/extensions/deduperreload/deduperreload.py

Lines 448 to 453 in dd41c52

    
           # exec new source code using old function's (obj) globals environment. 
        
           func_code = textwrap.dedent(ast.unparse(new_ast_def)) 
        
           if is_method := (len(prefixes) > 0): 
        
               func_code = "class __autoreload_class__:\n" + textwrap.indent( 
        
                   func_code, "    " 
        
               )

Something like this should preserve all the line number information from the source file:

@@ -446,11 +446,8 @@ def _patch_namespace_inner(
                 if isinstance(to_patch_to, (staticmethod, classmethod)):
                     to_patch_to = to_patch_to.__func__
                 # exec new source code using old function's (obj) globals environment.
-                func_code = textwrap.dedent(ast.unparse(new_ast_def))
                 if is_method := (len(prefixes) > 0):
-                    func_code = "class __autoreload_class__:\n" + textwrap.indent(
-                        func_code, "    "
-                    )
+                    new_ast_def = ast.ClassDef(name="__autoreload_class__", body=[new_ast_def])
                 global_env = ns.__dict__
                 if not isinstance(global_env, dict):
                     global_env = dict(global_env)
@@ -460,7 +457,7 @@ def _patch_namespace_inner(
                     and to_patch_to.__code__.co_filename
                     or "<string>"
                 )
-                func_asts = [ast.parse(func_code)]
+                func_asts = [new_ast_def]
                 if len(cast(ast.FunctionDef, func_asts[0].body[0]).decorator_list) > 0:
                     without_decorator_list = pickle.loads(pickle.dumps(func_asts[0]))
                     cast(

fix: preserve source line numbers in deduperreload reloaded functions

I've been testing out #15369 locally, and found a deeper issue: the traceback of a non-reloaded function can point to the wrong line if the function definition was moved around in the file due to added or removed lines before it.

It looks like it might be possible to update the function line numbers in-place with func.__code__ = func.__code__.replace(co_firstlineno=<new line number>).

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deduperreload gives invalid tracebacks in reloaded functions #15359

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	# exec new source code using old function's (obj) globals environment.
	func_code = textwrap.dedent(ast.unparse(new_ast_def))
	if is_method := (len(prefixes) > 0):
	func_code = "class __autoreload_class__:\n" + textwrap.indent(
	func_code, " "
	)

Sunbelt Computer Software

PL/B Language Development and Support

deduperreload gives invalid tracebacks in reloaded functions #15359

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yut23 commented on Aug 7, 2026

yut23 commented on Aug 16, 2026

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