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[OpenStack Infra <1565824@xxxxxxxxxxxxxxxxxx>]

Reviewed:  https://review.openstack.org/301166
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=ee53631886fff8c7e9d09b19b3456d0e80c5de88
Submitter: Jenkins
Branch:    master

commit ee53631886fff8c7e9d09b19b3456d0e80c5de88
Author: Markus Zoeller <mzoeller@xxxxxxxxxx>
Date:   Mon Apr 4 16:42:25 2016 +0200

    config option generation doesn't work with a generator
    
    The config options won't get emitted into "sample.config" when the
    "itertools.chain" method is used to combine multiple lists. The reason
    is that the generator created by "itertools.chain" doesn't get reset
    after getting used in "register_opts". A simple complete example:
    
        import itertools
    
        a = [1, 2]
        b = [3, 4]
    
        ab = itertools.chain(a, b)
    
        print("printing 'ab' for the first time")
        for i in ab:
            print(i)
    
        print("printing 'ab' for the second time")
        for i in ab:
            print(i)
    
    The combined list 'ab' won't get printed a second time. The same thing
    happens when the "oslo.config" generator wants to print the file
    "sample.config". The method "register_opts" gets called first and
    sets the cursor of the generator to the end, which means the same
    generator in "list_opts" is already at its end and iterates over
    nothing.
    
    This change creates a list with the generator. This list can be used
    multiple times, first by "register_opts" and then by "list_opts".
    The options get emitted into the "sample.config" file again.
    
    Closes bug 1565824
    Change-Id: Ib1bad2d76f34c5557b089f225511adfc0259fdb6


** Changed in: nova
       Status: In Progress => Fix Released

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https://bugs.launchpad.net/bugs/1565824

Title:
  config option generation doesn't work with itertools.chain generator

Status in OpenStack Compute (nova):
  Fix Released

Bug description:
  Config options code like this doesn't generate output in the
  sample.config file:

      ALL_OPTS = itertools.chain(
                 compute_opts,
                 resource_tracker_opts,
                 allocation_ratio_opts
                 )

  
      def register_opts(conf):
          conf.register_opts(ALL_OPTS)

  
      def list_opts():
          return {'DEFAULT': ALL_OPTS}

  The reason is that the generator created by "itertools.chain" doesn't
  get reset after getting used in "register_opts". A simple complete
  example:

      import itertools

      a = [1, 2]
      b = [3, 4]

      ab = itertools.chain(a, b)

      print("printing 'ab' for the first time")
      for i in ab:
  	    print(i)

      print("printing 'ab' for the second time")
      for i in ab:
  	    print(i)

  The combined list 'ab' won't get printed a second time. The same thing
  happens when the oslo.config generator wants to print the
  sample.config file. This means we use either:

      ab = list(itertools.chain(a, b))

  or

      ab = a + b

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