Merge #19674: refactor: test: use throwaway _ variable for unused loop counters

dac7a111bdd3b0233d94cf68dae7a8bfc6ac9c64 refactor: test: use _ variable for unused loop counters (Sebastian Falbesoner)

Pull request description:

  This tiny PR substitutes Python loops in the form of `for x in range(N): ...` by `for _ in range(N): ...` where applicable. The idea is indicating to the reader that a block (or statement, in list comprehensions) is just repeated N times, and that the loop counter is not used in the body, hence using the throwaway variable. This is already done quite often in the current tests (see e.g. `$ git grep "for _ in range("`). Another alternative would be using `itertools.repeat` (according to Python core developer Raymond Hettinger it's [even faster](https://twitter.com/raymondh/status/1144527183341375488)), but that doesn't seem to be widespread in use and I'm not sure about a readability increase.

  The only drawback I see is that whenever one wants to debug loop iterations, one would need to introduce a loop variable again. Reviewing this is basically a no-brainer, since tests would fail immediately if a a substitution has taken place on a loop where the variable is used.

  Instances to replace were found by `$ git grep "for.*in range("` and manually checked.

ACKs for top commit:
  darosior:
    ACK dac7a111bdd3b0233d94cf68dae7a8bfc6ac9c64
  instagibbs:
    manual inspection ACK https://github.com/bitcoin/bitcoin/pull/19674/commits/dac7a111bdd3b0233d94cf68dae7a8bfc6ac9c64
  practicalswift:
    ACK dac7a111bdd3b0233d94cf68dae7a8bfc6ac9c64 -- the updated code is easier to reason about since the throwaway nature of a variable is expressed explicitly (using the Pythonic `_` idiom) instead of implicitly. Explicit is better than implicit was we all know by now :)

Tree-SHA512: 5f43ded9ce14e5e00b3876ec445b90acda1842f813149ae7bafa93f3ac3d510bb778e2c701187fd2c73585e6b87797bb2d2987139bd1a9ba7d58775a59392406

1 files changed, 1 insertions, 1 deletions

diff --git a/test/functional/mempool_persist.py b/test/functional/mempool_persist.py
index 5d00648aed..85c4d6d570 100755
--- a/test/functional/mempool_persist.py
+++ b/test/functional/mempool_persist.py
@@ -62,7 +62,7 @@ class MempoolPersistTest(BitcoinTestFramework):
     def run_test(self):
         self.log.debug("Send 5 transactions from node2 (to its own address)")
         tx_creation_time_lower = int(time.time())
-        for i in range(5):
+        for _ in range(5):
             last_txid = self.nodes[2].sendtoaddress(self.nodes[2].getnewaddress(), Decimal("10"))
         node2_balance = self.nodes[2].getbalance()
         self.sync_all()