implemented Coin::opreturn method

Author: peerchemist

pacli/coin.py

@@ -5,6 +5,7 @@
 from pypeerassets.networks import net_query
 from pypeerassets.transactions import (tx_output,
                                        p2pkh_script,
+                                       nulldata_script,
                                        make_raw_transaction,
                                        Locktime)
 
@@ -55,3 +56,36 @@ def sendto(self, address: Union[str], amount: Union[float],
         signedtx = sign_transaction(provider, unsigned_tx, Settings.key)
 
         return sendtx(signedtx)
+
+    def opreturn(self, string: hex, locktime: int=0) -> str:
+        '''send op_return transaction'''
+
+        network_params = net_query(Settings.network)
+
+        inputs = provider.select_inputs(Settings.key.address, 0.01)
+
+        outs = [tx_output(network=provider.network,
+                          value=Decimal(0), n=1,
+                          script=nulldata_script(bytes.fromhex(string))
+                          )
+                ]
+
+        #  first round of txn making is done by presuming minimal fee
+        change_sum = Decimal(inputs['total'] - network_params.min_tx_fee)
+
+        outs.append(
+            tx_output(network=provider.network,
+                      value=change_sum, n=len(outs)+1,
+                      script=p2pkh_script(address=Settings.key.address,
+                                          network=provider.network))
+                    )
+
+        unsigned_tx = make_raw_transaction(network=provider.network,
+                                           inputs=inputs['utxos'],
+                                           outputs=outs,
+                                           locktime=Locktime(locktime)
+                                           )
+
+        signedtx = sign_transaction(provider, unsigned_tx, Settings.key)
+
+        return sendtx(signedtx)