Summary
On Windows systems with non-UTF-8 default encoding (e.g., cp1252), the first execution of the magic command %load_ext autoreload in a Jupyter notebook fails with a UnicodeDecodeError when the IPython extension deduperreload attempts to read Python Standard Library module files.
Environment
- IPython version: 9.10.0
- Python version: 3.13.11
- Platform: Windows
- System default encoding:
cp1252 (Windows-1252)
- Jupyter: JupyterLab / VS Code Notebooks
Error Description
When running %load_ext autoreload for the first time in a fresh IPython kernel, the following traceback is printed:
Failed to read module file 'C:...\python\Lib\urllib\parse.py' for module 'urllib.parse': UnicodeDecodeError
...
ModuleNotFoundError: No module named 'autoreload'
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "c:...\venv\Lib\site-packages\IPython\extensions\deduperreload\deduperreload.py", line 219, in update_sources
self.source_by_modname[new_modname] = f.read()
File "C:...\python\Lib\encodings\cp1252.py", line 23, in decode
return codecs.charmap_decode(input,self.errors,decoding_table)[0]
UnicodeDecodeError: 'charmap' codec can't decode byte 0x9d in position 1981: character maps to <undefined>
This error is repeated for multiple Standard Library modules (e.g., functools.py, re._casefix.py, _strptime.py).
Workaround: Running the command a second time succeeds without errors.
Root Cause
In IPython/extensions/deduperreload/deduperreload.py, line 219, the update_sources() method opens Python module files without specifying an encoding:
with open(fname, "r") as f:
self.source_by_modname[new_modname] = f.read()Proposed Fix
Explicitly specify encoding="utf-8" in the file open operation:
--- a/IPython/extensions/deduperreload/deduperreload.py
+++ b/IPython/extensions/deduperreload/deduperreload.py
@@ -216,7 +216,7 @@ class SourceDiffChecker:
continue
try:
- with open(fname, "r") as f:
+ with open(fname, "r", encoding="utf-8", errors="replace") as f:
self.source_by_modname[new_modname] = f.read()
except Exception as e:
logger = logging.getLogger("autoreload")
Summary
On Windows systems with non-UTF-8 default encoding (e.g.,
cp1252), the first execution of the magic command%load_ext autoreloadin a Jupyter notebook fails with aUnicodeDecodeErrorwhen the IPython extensiondeduperreloadattempts to read Python Standard Library module files.Environment
cp1252(Windows-1252)Error Description
When running
%load_ext autoreloadfor the first time in a fresh IPython kernel, the following traceback is printed:This error is repeated for multiple Standard Library modules (e.g.,
functools.py,re._casefix.py,_strptime.py).Workaround: Running the command a second time succeeds without errors.
Root Cause
In
IPython/extensions/deduperreload/deduperreload.py, line 219, theupdate_sources()method opens Python module files without specifying an encoding:Proposed Fix
Explicitly specify
encoding="utf-8"in the file open operation: