refactor: test: use _ variable for unused loop counters

substitutes "for x in range(N):" by "for _ in range(N):"
indicates to the reader that a block is just repeated N times, and
that the loop counter is not used in the body

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