Added payment info function for fee estimation #45

substrateinterface/__init__.py

@@ -1117,18 +1117,18 @@ def create_signed_extrinsic(self, call, keypair: Keypair, era=None, nonce=None,
             raise TypeError("'call' must be of type Call")
 
         # Retrieve nonce
-        if not nonce:
+        if nonce is None:
             nonce = self.get_account_nonce(keypair.public_key) or 0
 
         # Process era
-        if not era:
+        if era is None:
             era = '00'
         else:
             if isinstance(era, dict) and 'current' not in era and 'phase' not in era:
                 # Retrieve current block id
                 era['current'] = self.get_block_number(self.get_chain_finalised_head())
 
-        if signature:
+        if signature is not None:
 
             signature = signature.replace('0x', '')
 
@@ -1237,6 +1237,49 @@ def result_handler(result):
 
         return response
 
+    def get_payment_info(self, call, keypair):
+        """
+        Retrieves fee estimation via RPC for given extrinsic
+
+        Parameters
+        ----------
+        call Call object to estimate fees for
+        keypair Keypair of the sender, does not have to include private key because no valid signature is required
+
+        Returns
+        -------
+        Dict with payment info
+
+        E.g. {'class': 'normal', 'partialFee': 151000000, 'weight': 217238000}
+
+        """
+
+        # Check requirements
+        if not isinstance(call, GenericCall):
+            raise TypeError("'call' must be of type Call")
+
+        if not isinstance(keypair, Keypair):
+            raise TypeError("'keypair' must be of type Keypair")
+
+        # No valid signature is required for fee estimation
+        signature = '0x' + '00' * 64
+
+        # Create extrinsic
+        extrinsic = self.create_signed_extrinsic(
+            call=call,
+            keypair=keypair,
+            signature=signature
+        )
+
+        payment_info = self.rpc_request('payment_queryInfo', [str(extrinsic.data)])
+
+        # convert partialFee to int
+        if 'result' in payment_info:
+            payment_info['result']['partialFee'] = int(payment_info['result']['partialFee'])
+            return payment_info['result']
+        else:
+            raise SubstrateRequestException(payment_info['error']['message'])
+
     def process_metadata_typestring(self, type_string):
         """
         Process how given type_string is decoded with active runtime and type registry

test/test_create_extrinsics.py

@@ -129,6 +129,25 @@ def test_create_unsigned_extrinsic(self):
         extrinsic = self.kusama_substrate.create_unsigned_extrinsic(call)
         self.assertEqual(str(extrinsic.data), '0x280402000ba09cc0317501')
 
+    def test_payment_info(self):
+        keypair = Keypair(ss58_address="EaG2CRhJWPb7qmdcJvy3LiWdh26Jreu9Dx6R1rXxPmYXoDk")
+
+        call = self.kusama_substrate.compose_call(
+            call_module='Balances',
+            call_function='transfer',
+            call_params={
+                'dest': 'EaG2CRhJWPb7qmdcJvy3LiWdh26Jreu9Dx6R1rXxPmYXoDk',
+                'value': 2 * 10 ** 3
+            }
+        )
+        payment_info = self.kusama_substrate.get_payment_info(call=call, keypair=keypair)
+
+        self.assertIn('class', payment_info)
+        self.assertIn('partialFee', payment_info)
+        self.assertIn('weight', payment_info)
+
+        self.assertGreater(payment_info['partialFee'], 0)
+
 
 if __name__ == '__main__':
     unittest.main()