[tor-bugs] #20579 [Metrics/Torflow]: TorCtl re-uses iterables, even though they only yield their items once

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#20579: TorCtl re-uses iterables, even though they only yield their items once
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     Reporter:  teor             |      Owner:  aagbsn
         Type:  defect           |     Status:  new
     Priority:  Medium           |  Milestone:
    Component:  Metrics/Torflow  |    Version:
     Severity:  Major            |   Keywords:
Actual Points:                   |  Parent ID:
       Points:                   |   Reviewer:
      Sponsor:                   |
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 When TorCtl calls filter(), it often re-uses the iterable multiple times.
 But python iterables only yield each item once.
 To fix this, we need to turn iterables we want to re-use into a list,
 using list(filter()).

 This might just be why a lot of nodes remain unmeasured, or measurement is
 unreliable. In our test network, it seems to have caused only 5-7/15 nodes
 to be measured.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/20579>
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