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

dac7a11 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 dac7a11
  instagibbs:
    manual inspection ACK bitcoin/bitcoin@dac7a11
  practicalswift:
    ACK dac7a11 -- 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

Author: fanquake

test/functional/example_test.py

@@ -166,7 +166,7 @@ def run_test(self):
 
         height = self.nodes[0].getblockcount()
 
-        for i in range(10):
+        for _ in range(10):
             # Use the mininode and blocktools functionality to manually build a block
             # Calling the generate() rpc is easier, but this allows us to exactly
             # control the blocks and transactions.

test/functional/feature_assumevalid.py

@@ -123,7 +123,7 @@ def run_test(self):
         height += 1
 
         # Bury the block 100 deep so the coinbase output is spendable
-        for i in range(100):
+        for _ in range(100):
             block = create_block(self.tip, create_coinbase(height), self.block_time)
             block.solve()
             self.blocks.append(block)
@@ -149,7 +149,7 @@ def run_test(self):
         height += 1
 
         # Bury the assumed valid block 2100 deep
-        for i in range(2100):
+        for _ in range(2100):
             block = create_block(self.tip, create_coinbase(height), self.block_time)
             block.nVersion = 4
             block.solve()

test/functional/feature_bip68_sequence.py

@@ -141,7 +141,7 @@ def test_sequence_lock_confirmed_inputs(self):
         # some of those inputs to be sequence locked (and randomly choose
         # between height/time locking). Small random chance of making the locks
         # all pass.
-        for i in range(400):
+        for _ in range(400):
             # Randomly choose up to 10 inputs
             num_inputs = random.randint(1, 10)
             random.shuffle(utxos)
@@ -260,7 +260,7 @@ def test_nonzero_locks(orig_tx, node, relayfee, use_height_lock):
         # Use prioritisetransaction to lower the effective feerate to 0
         self.nodes[0].prioritisetransaction(txid=tx2.hash, fee_delta=int(-self.relayfee*COIN))
         cur_time = int(time.time())
-        for i in range(10):
+        for _ in range(10):
             self.nodes[0].setmocktime(cur_time + 600)
             self.nodes[0].generate(1)
             cur_time += 600

test/functional/feature_block.py

@@ -125,7 +125,7 @@ def run_test(self):
 
         # collect spendable outputs now to avoid cluttering the code later on
         out = []
-        for i in range(NUM_OUTPUTS_TO_COLLECT):
+        for _ in range(NUM_OUTPUTS_TO_COLLECT):
             out.append(self.get_spendable_output())
 
         # Start by building a couple of blocks on top (which output is spent is

test/functional/feature_csv_activation.py

@@ -161,7 +161,7 @@ def skip_test_if_missing_module(self):
 
     def generate_blocks(self, number):
         test_blocks = []
-        for i in range(number):
+        for _ in range(number):
             block = self.create_test_block([])
             test_blocks.append(block)
             self.last_block_time += 600
@@ -209,22 +209,22 @@ def run_test(self):
         # Note we reuse inputs for v1 and v2 txs so must test these separately
         # 16 normal inputs
         bip68inputs = []
-        for i in range(16):
+        for _ in range(16):
             bip68inputs.append(send_generic_input_tx(self.nodes[0], self.coinbase_blocks, self.nodeaddress))
 
         # 2 sets of 16 inputs with 10 OP_CSV OP_DROP (actually will be prepended to spending scriptSig)
         bip112basicinputs = []
-        for j in range(2):
+        for _ in range(2):
             inputs = []
-            for i in range(16):
+            for _ in range(16):
                 inputs.append(send_generic_input_tx(self.nodes[0], self.coinbase_blocks, self.nodeaddress))
             bip112basicinputs.append(inputs)
 
         # 2 sets of 16 varied inputs with (relative_lock_time) OP_CSV OP_DROP (actually will be prepended to spending scriptSig)
         bip112diverseinputs = []
-        for j in range(2):
+        for _ in range(2):
             inputs = []
-            for i in range(16):
+            for _ in range(16):
                 inputs.append(send_generic_input_tx(self.nodes[0], self.coinbase_blocks, self.nodeaddress))
             bip112diverseinputs.append(inputs)
 

test/functional/feature_dbcrash.py

@@ -195,7 +195,7 @@ def generate_small_transactions(self, node, count, utxo_list):
         while len(utxo_list) >= 2 and num_transactions < count:
             tx = CTransaction()
             input_amount = 0
-            for i in range(2):
+            for _ in range(2):
                 utxo = utxo_list.pop()
                 tx.vin.append(CTxIn(COutPoint(int(utxo['txid'], 16), utxo['vout'])))
                 input_amount += int(utxo['amount'] * COIN)
@@ -205,7 +205,7 @@ def generate_small_transactions(self, node, count, utxo_list):
                 # Sanity check -- if we chose inputs that are too small, skip
                 continue
 
-            for i in range(3):
+            for _ in range(3):
                 tx.vout.append(CTxOut(output_amount, hex_str_to_bytes(utxo['scriptPubKey'])))
 
             # Sign and send the transaction to get into the mempool

test/functional/feature_fee_estimation.py

@@ -176,9 +176,9 @@ def transact_and_mine(self, numblocks, mining_node):
         # We shuffle our confirmed txout set before each set of transactions
         # small_txpuzzle_randfee will use the transactions that have inputs already in the chain when possible
         # resorting to tx's that depend on the mempool when those run out
-        for i in range(numblocks):
+        for _ in range(numblocks):
             random.shuffle(self.confutxo)
-            for j in range(random.randrange(100 - 50, 100 + 50)):
+            for _ in range(random.randrange(100 - 50, 100 + 50)):
                 from_index = random.randint(1, 2)
                 (txhex, fee) = small_txpuzzle_randfee(self.nodes[from_index], self.confutxo,
                                                       self.memutxo, Decimal("0.005"), min_fee, min_fee)
@@ -243,7 +243,7 @@ def run_test(self):
         self.confutxo = self.txouts  # Start with the set of confirmed txouts after splitting
         self.log.info("Will output estimates for 1/2/3/6/15/25 blocks")
 
-        for i in range(2):
+        for _ in range(2):
             self.log.info("Creating transactions and mining them with a block size that can't keep up")
             # Create transactions and mine 10 small blocks with node 2, but create txs faster than we can mine
             self.transact_and_mine(10, self.nodes[2])

test/functional/feature_maxuploadtarget.py

@@ -104,7 +104,7 @@ def run_test(self):
         assert_equal(len(self.nodes[0].getpeerinfo()), 3)
         # At most a couple more tries should succeed (depending on how long
         # the test has been running so far).
-        for i in range(3):
+        for _ in range(3):
             p2p_conns[0].send_message(getdata_request)
         p2p_conns[0].wait_for_disconnect()
         assert_equal(len(self.nodes[0].getpeerinfo()), 2)

test/functional/feature_pruning.py

@@ -147,7 +147,7 @@ def create_chain_with_staleblocks(self):
         # Create stale blocks in manageable sized chunks
         self.log.info("Mine 24 (stale) blocks on Node 1, followed by 25 (main chain) block reorg from Node 0, for 12 rounds")
 
-        for j in range(12):
+        for _ in range(12):
             # Disconnect node 0 so it can mine a longer reorg chain without knowing about node 1's soon-to-be-stale chain
             # Node 2 stays connected, so it hears about the stale blocks and then reorg's when node0 reconnects
             disconnect_nodes(self.nodes[0], 1)

test/functional/feature_rbf.py

@@ -376,7 +376,7 @@ def test_too_many_replacements(self):
         split_value = int((initial_nValue-fee)/(MAX_REPLACEMENT_LIMIT+1))
 
         outputs = []
-        for i in range(MAX_REPLACEMENT_LIMIT+1):
+        for _ in range(MAX_REPLACEMENT_LIMIT+1):
             outputs.append(CTxOut(split_value, CScript([1])))
 
         splitting_tx = CTransaction()