[issue3458] dict.update() optimisation gives unexpected/invalid results when passed a subclass of DictType

[Raymond Hettinger]

Raymond Hettinger <rhettinger at users.sourceforge.net> added the comment:

This is duplicate of http://bugs.python.org/issue1615701 .  The 
check_exact solution was attempted once but it broke code in a subtle 
and hard to find way so it had to be reverted.  For your use case, try 
UserDict instead of subclassing dict.

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resolution:  -> duplicate
status: open -> closed

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