Prepare to calculate tx fee given a tx size

lib/coinchooser.py

@@ -32,8 +32,7 @@ class CoinChooser(PrintError):
         added to the transaction fee.'''
         amount = sum(map(lambda x: x[2], outputs))
         total = 0
-        inputs = []
-        tx = Transaction.from_io(inputs, outputs)
+        tx = Transaction.from_io([], outputs)
         fee = fee_estimator(tx)
         # add inputs, sorted by age
         for item in coins:

lib/transaction.py

@@ -689,14 +689,22 @@ class Transaction:
     def get_fee(self):
         return self.input_value() - self.output_value()
 
-    @profiler
-    def estimated_fee(self, fee_per_kb):
-        estimated_size = len(self.serialize(-1)) / 2
-        fee = int(fee_per_kb * estimated_size / 1000.)
+    @classmethod
+    def estimated_fee_for_size(self, fee_per_kb, size):
+        '''Given a fee per kB in satoshis, and a tx size in bytes,
+        returns the transaction fee.'''
+        fee = int(fee_per_kb * size / 1000.)
         if fee < MIN_RELAY_TX_FEE:
             fee = MIN_RELAY_TX_FEE
         return fee
 
+    @profiler
+    def estimated_fee(self, fee_per_kb):
+        '''Return an estimated fee given a fee per kB in satoshis.'''
+        # Remember self.serialize returns an ASCII hex string
+        size = len(self.serialize(-1)) / 2
+        return self.estimated_fee_for_size(fee_per_kb, size)
+
     def signature_count(self):
         r = 0
         s = 0

lib/wallet.py

@@ -927,11 +927,14 @@ class Abstract_Wallet(PrintError):
             else:
                 change_addrs = [address]
 
-        fee_per_kb = self.fee_per_kb(config)
-        def fee_estimator(tx):
-            if fixed_fee is not None:
+        # Fee estimator
+        if fixed_fee is None:
+            fee_per_kb = self.fee_per_kb(config)
+            def fee_estimator(tx):
+                return tx.estimated_fee(fee_per_kb)
+        else:
+            def fee_estimator(tx):
                 return fixed_fee
-            return tx.estimated_fee(fee_per_kb)
 
         # Change <= dust threshold is added to the tx fee
         dust_threshold = 182 * 3 * MIN_RELAY_TX_FEE / 1000