[docs] [issue30211] Bdb: add docstrings

[Terry J. Reedy]

Terry J. Reedy added the comment:

In the entry at https://docs.python.org/3/library/bdb.html#bdb.Bdb.canonic, 
", stripped of surrounding angle brackets"
is wrong, and should be replaced by
".  'Filenames' with angle brackets, such as "<stdin>", generated in interactive mode, are returned unchanged"

>>> 1/0
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ZeroDivisionError: division by zero

(IDLE generates "<PyShell#n>", when n is statement number, starting with 0.)

This and any other doc errors we find should be corrected in this issue, but perhaps in a separate PR that can be backported separately.

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assignee: docs at python -> terry.reedy

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue30211>
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