BIND 10 #934: use real constants (instead of proxy factory) in pydnspp

[BIND 10 Development]

#934: use real constants (instead of proxy factory) in pydnspp
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            Reporter:  jinmei        |                        Owner:
                Type:  enhancement   |  jinmei
            Priority:  major         |                       Status:  new
           Component:  DNSPacket     |                    Milestone:  New
  API                                |  Tasks
           Sensitive:  0             |                     Keywords:
         Sub-Project:  DNS           |              Defect Severity:  N/A
Estimated Difficulty:  0             |  Feature Depending on Ticket:
         Total Hours:  0             |          Add Hours to Ticket:  0
                                     |                    Internal?:  0
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 I noticed that pydnspp uses many proxy factory functions for constant
 objects like RRType.AAAA(), RRClass.IN().  In Python we don't have to
 do that because there's no worry for static initialization fiasco
 (which is the reason why we use the proxy functions in C++).

 We can simply define RRType.AAAA, etc, as class constant in
 initialization and use it throughout our applications.  That will be
 more intuitive, and will be a bit more efficient (a call to a proxy
 function always involve an allocation of PyObject and subsequent
 deallocation; real constants are created only once in initialization).

 I'd propose making this change in the entire pydnspp.  It will require
 changes to the applications (xfrin.py, etc), but the changes should be
 pretty straightforward.

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Ticket URL: <http://bind10.isc.org/ticket/934>
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