New submission from Martin Panter:
I made a writer class whose write() and flush() methods (unintentionally)
triggered exceptions. I wrapped this in a BufferedWriter. When close() is
called, the resulting exception has a string object in its __context__
attribute. Although the original error was my fault, it created a confusing
chain reaction of exception reports.
>>> from io import BufferedWriter, RawIOBase
>>> import sys
>>>
>>> class BuggyWriter(RawIOBase):
... def writable(self): return True
... def write(self, b): in_write # Initial exception
... def flush(self): raise Exception("In flush()")
...
>>> output = BufferedWriter(BuggyWriter())
>>> output.write(b"data")
4
>>> output.close() # Note the TypeError printed at the top
TypeError: print_exception(): Exception expected for value, str found
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<stdin>", line 4, in flush
Exception: In flush()
>>>
>>> sys.last_value
Exception('In flush()',)
>>> sys.last_value.__context__ # Should be exception, not string object
"name 'in_write' is not defined"
>>>
>>> import traceback
>>> traceback.print_exception(sys.last_type, sys.last_value, sys.last_traceback)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/usr/lib/python3.4/traceback.py", line 169, in print_exception
for line in _format_exception_iter(etype, value, tb, limit, chain):
File "/usr/lib/python3.4/traceback.py", line 146, in _format_exception_iter
for value, tb in values:
File "/usr/lib/python3.4/traceback.py", line 138, in _iter_chain
yield from it
File "/usr/lib/python3.4/traceback.py", line 125, in _iter_chain
context = exc.__context__
AttributeError: 'str' object has no attribute '__context__'
----------
components: IO
messages: 219864
nosy: vadmium
priority: normal
severity: normal
status: open
title: Exception context set to string by BufferedWriter.close()
type: behavior
versions: Python 3.4
_______________________________________
Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue21677>
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