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, 6 insertions, 6 deletions

diff --git a/test/functional/p2p_sendheaders.py b/test/functional/p2p_sendheaders.py
index 481b1c1841..126a46bd53 100755
--- a/test/functional/p2p_sendheaders.py
+++ b/test/functional/p2p_sendheaders.py
@@ -328,7 +328,7 @@ class SendHeadersTest(BitcoinTestFramework):
             for j in range(2):
                 self.log.debug("Part 2.{}.{}: starting...".format(i, j))
                 blocks = []
-                for b in range(i + 1):
+                for _ in range(i + 1):
                     blocks.append(create_block(tip, create_coinbase(height), block_time))
                     blocks[-1].solve()
                     tip = blocks[-1].sha256
@@ -443,7 +443,7 @@ class SendHeadersTest(BitcoinTestFramework):
 
         # Create 2 blocks.  Send the blocks, then send the headers.
         blocks = []
-        for b in range(2):
+        for _ in range(2):
             blocks.append(create_block(tip, create_coinbase(height), block_time))
             blocks[-1].solve()
             tip = blocks[-1].sha256
@@ -461,7 +461,7 @@ class SendHeadersTest(BitcoinTestFramework):
 
         # This time, direct fetch should work
         blocks = []
-        for b in range(3):
+        for _ in range(3):
             blocks.append(create_block(tip, create_coinbase(height), block_time))
             blocks[-1].solve()
             tip = blocks[-1].sha256
@@ -482,7 +482,7 @@ class SendHeadersTest(BitcoinTestFramework):
         blocks = []
 
         # Create extra blocks for later
-        for b in range(20):
+        for _ in range(20):
             blocks.append(create_block(tip, create_coinbase(height), block_time))
             blocks[-1].solve()
             tip = blocks[-1].sha256
@@ -529,7 +529,7 @@ class SendHeadersTest(BitcoinTestFramework):
             test_node.last_message.pop("getdata", None)
             blocks = []
             # Create two more blocks.
-            for j in range(2):
+            for _ in range(2):
                 blocks.append(create_block(tip, create_coinbase(height), block_time))
                 blocks[-1].solve()
                 tip = blocks[-1].sha256
@@ -550,7 +550,7 @@ class SendHeadersTest(BitcoinTestFramework):
         # Now we test that if we repeatedly don't send connecting headers, we
         # don't go into an infinite loop trying to get them to connect.
         MAX_UNCONNECTING_HEADERS = 10
-        for j in range(MAX_UNCONNECTING_HEADERS + 1):
+        for _ in range(MAX_UNCONNECTING_HEADERS + 1):
             blocks.append(create_block(tip, create_coinbase(height), block_time))
             blocks[-1].solve()
             tip = blocks[-1].sha256