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This proposal would be useful. My use case is for when an API suppresses an external exception context:
>>> import os
>>> try:
... os.environ["NEW_VARIABLE"] = bug # Hidden exception
... finally:
... del os.environ["NEW_VARIABLE"] # KeyError
... 
Traceback (most recent call last):
 File "<stdin>", line 4, in <module>
 File "/usr/lib/python3.5/os.py", line 699, in __delitem__
 raise KeyError(key) from None
KeyError: 'NEW_VARIABLE'
This feels like a step backwards to Python 2, and enabling the full backtrace would make this easier to analyze:
>>> try:
... os.environ["NEW_VARIABLE"] = bug # TypeError
... finally:
... del dict()["NEW_VARIABLE"] # KeyError
... 
Traceback (most recent call last):
 File "<stdin>", line 2, in <module>
 File "/usr/lib/python3.5/os.py", line 688, in __setitem__
 value = self.encodevalue(value)
 File "/usr/lib/python3.5/os.py", line 756, in encode
 raise TypeError("str expected, not %s" % type(value).__name__)
TypeError: str expected, not object
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
 File "<stdin>", line 4, in <module>
KeyError: 'NEW_VARIABLE'