Handling exception chaining and raising from context

>>> def func():
...     raise ConnectionError
...
>>> try:
...     func()
... except ConnectionError as exc:
...     raise RuntimeError('Failed to open database') from exc
...
Traceback (most recent call last):
  File "<stdin>", line 2, in <module>
  File "<stdin>", line 2, in func
ConnectionError
 
The above exception was the direct cause of the following exception:
 
Traceback (most recent call last):
  File "<stdin>", line 4, in <module>
RuntimeError: Failed to open database

try:
    open('database.sqlite')
except OSError:
    raise RuntimeError from None
 
Traceback (most recent call last):
  File "<stdin>", line 4, in <module>
RuntimeError