[tests] Recommend f-strings for formatting, update feature_block to use them

1 files changed, 5 insertions, 5 deletions

diff --git a/test/functional/feature_block.py b/test/functional/feature_block.py
index 3cf7f3890c..158efb52c9 100755
--- a/test/functional/feature_block.py
+++ b/test/functional/feature_block.py
@@ -119,7 +119,7 @@ class FullBlockTest(BitcoinTestFramework):
         # Allow the block to mature
         blocks = []
         for i in range(NUM_BUFFER_BLOCKS_TO_GENERATE):
-            blocks.append(self.next_block("maturitybuffer.{}".format(i)))
+            blocks.append(self.next_block(f"maturitybuffer.{i}"))
             self.save_spendable_output()
         self.send_blocks(blocks)
 
@@ -151,8 +151,8 @@ class FullBlockTest(BitcoinTestFramework):
             if template.valid_in_block:
                 continue
 
-            self.log.info("Reject block with invalid tx: %s", TxTemplate.__name__)
-            blockname = "for_invalid.%s" % TxTemplate.__name__
+            self.log.info(f"Reject block with invalid tx: {TxTemplate.__name__}")
+            blockname = f"for_invalid.{TxTemplate.__name__}"
             badblock = self.next_block(blockname)
             badtx = template.get_tx()
             if TxTemplate != invalid_txs.InputMissing:
@@ -1355,12 +1355,12 @@ class FullBlockTest(BitcoinTestFramework):
 
     # save the current tip so it can be spent by a later block
     def save_spendable_output(self):
-        self.log.debug("saving spendable output %s" % self.tip.vtx[0])
+        self.log.debug(f"saving spendable output {self.tip.vtx[0]}")
         self.spendable_outputs.append(self.tip)
 
     # get an output that we previously marked as spendable
     def get_spendable_output(self):
-        self.log.debug("getting spendable output %s" % self.spendable_outputs[0].vtx[0])
+        self.log.debug(f"getting spendable output {self.spendable_outputs[0].vtx[0]}")
         return self.spendable_outputs.pop(0).vtx[0]
 
     # move the tip back to a previous block