# 17.4: Accessing Bitcoind with Python

> :information_source: **NOTE:** This is a draft in progress, so that I can get some feedback from early reviewers. It is not yet ready for learning.

This section explains how to interact with `bitcoind` using the Python programming language and the [Python-BitcoinRPC](https://github.com/jgarzik/python-bitcoinrpc).

## Setting Up Python

If you already have Bitcoin Core installed, you should have Python 3 available as well.
You can check this by running:

`$ python3 --version`

If it returns a version number (e.g., `3.7.3` or `3.8.3`) then you have python3 installed. 

However, if you somehow do not have Python installed, you'll need build it from source as follows. Please see ["Building Python from Source"](17_4_Accessing_Bitcoind_with_Python.md#synopsis-building-python-from-source) before continuing.

### Setting Up BitcoinRPC

Whether you used an existing Python or built it from source, you're now ready to install  the `python-bitcoinrpc` library:

```
$ pip3 install python-bitcoinrpc
```
If you don't have `pip` installed, you'll need to run the following:
```
$ sudo apt install python3-pip
```
(Then repeat the `pip3 install python-bitcoinrpc` instructions.)

### Creating a BitcoinRPC Project

You'll generally need to include appropriate declarations from `bitcoinrpc` in your Bitcoin projects in Python. The following will give you access to the RPC based commands:
```py
from bitcoinrpc.authproxy import AuthServiceProxy, JSONRPCException
```
You may also find the following useful:
```py
from pprint import pprint
import logging
```
`pprint` will pretty print the `json` response from `bitcoind`.

`logging` will print out the call you make to `bitcoind` and `bitcoind`'s respose, which is useful when you make a bunch of calls together. If you don't want the excessive output in the terminal just comment out the `logging` block.

## Building Your Connection

You are now ready to start interacting with `bitcoind` by establishing a connection. Create a file called `btcrpc.py` and type the following:

```py
logging.basicConfig()
logging.getLogger("BitcoinRPC").setLevel(logging.DEBUG)
# rpc_user and rpc_password are set in the bitcoin.conf file
rpc_user = "StandUp"
rpc_pass = "6305f1b2dbb3bc5a16cd0f4aac7e1eba"
rpc_host = "127.0.0.1"
rpc_client = AuthServiceProxy(f"http://{rpc_user}:{rpc_pass}@{rpc_host}:18332", timeout=120)
```

The arguments in the URL are `<rpc_username>:<rpc_password>@<host_IP_address>:<port>`. As usual, the `user` and `pass` are found in your `~/.bitcoin/bitcoin.conf`, while the `host` is your localhost, and the port is `18332` for testnet. The `timeout` argument is specified since sockets timeout under heavy load on the mainnet. If you get `socket.timeout: timed out` response, be patient and increase the `timeout`.

> :link: MAINNET VS TESTNET: The port would be 8332 for a mainnet setup.

### Making  an RPC Call

If `rpc_client` is successfully initialized, you'll be able to send off RPC commands to your bitcoin node.

In order to use an RPC method from `python-bitcoinrpc`, you'll use `rpc_client` object that you created, which provides most of the functionality that can be accessed through `bitcoin-cli`, using the same method names.

For example, the following will retrieve the blockcount of your node:

```py
block_count = rpc_client.getblockcount()
print("---------------------------------------------------------------")
print("Block Count:", block_count)
print("---------------------------------------------------------------\n")
```

You should see the following output with `logging` enabled :

```sh
DEBUG:BitcoinRPC:-3-> getblockcount []
DEBUG:BitcoinRPC:<-3- 1773020
---------------------------------------------------------------
Block Count: 1773020
---------------------------------------------------------------
```
### Making an RPC Call with Arguments

You can use that blockcount as an argument to retrieve the blockhash of a block and also to retrieve details of that block.

This is done by send your `rpc_client` object commands with an argument:
```py
blockhash = rpc_client.getblockhash(block_count)
block = rpc_client.getblock(blockhash)
```

The `getblockhash` will return a single value, while the `getblock` will return an associative array of information about the block, which includes an array under `block['tx']` providing details on each transaction within the block:
```py
nTx = block['nTx']
if nTx > 10:
    it_txs = 10
    list_tx_heading = "First 10 transactions: "
else:
    it_txs = nTx
    list_tx_heading = f"All the {it_txs} transactions: "
print("---------------------------------------------------------------")
print("BLOCK: ", block_count)
print("-------------")
print("Block Hash...: ", blockhash)
print("Merkle Root..: ", block['merkleroot'])
print("Block Size...: ", block['size'])
print("Block Weight.: ", block['weight'])
print("Nonce........: ", block['nonce'])
print("Difficulty...: ", block['difficulty'])
print("Number of Tx.: ", nTx)
print(list_tx_heading)
print("---------------------")
i = 0
while i < it_txs:
    print(i, ":", block['tx'][i])
    i += 1
print("---------------------------------------------------------------\n")
```

### Running Your Code

You can retrieve [the src code](src/17_4_getinfo.py) and run it with `python3`:
```
$ python3 getinfo.py
---------------------------------------------------------------
Block Count: 1831106
---------------------------------------------------------------
---------------------------------------------------------------
BLOCK:  1831106
-------------
Block Hash...:  00000000000003b2ea7c2cdfffd86156ad1f5606ab58e128940a2534d1348b04
Merkle Root..:  056a547fe59208167eef86fa694263728fb684119254b340c1f86bdd423a8082
Block Size...:  52079
Block Weight.:  128594
Nonce........:  1775583700
Difficulty...:  4194304
Number of Tx.:  155
First 10 transactions: 
---------------------
0 : d228d55112e3aa26265b0118cfdc98345c229d20fe074b9afb87107c03ce11b5
1 : 92822e8e34fafb472b87c99ea3f3e16440452b3f361ed86c6fa62175173fb750
2 : fa7c67600c14d4aa350a9674688f1429577954f4a6c5e4639d06c8964824f647
3 : 3a91d1527e308e5603dafde7ab17824f441a73a779d2571d073466dc9e8451b2
4 : 30fd0e5527b1522e7b26a4818b9edac80fe47c0c39fc34705478a49e684708d0
5 : 24c5372b38c78cbaf5b0b305925502a491bc0c1b5758f50c0bd335abb6ae85f5
6 : be70e125a5793efc5e32051fecba0668df971bdf371138c8261201c2a46b2d38
7 : 41ebf52c847a59ba0aeb4425c74e89a01e91defa86a82785ff53ed4668054561
8 : dc8211b4ce122f87692e7c203672e3eb1ffc44c0a307eafcc560323fcc5fae78
9 : 59e2d8e11cad287eacf3207e64a373f65059286b803ef0981510193ae29cbc8c
---------------------------------------------------------------
```

## Looking Up Funds

You can similarly retrieve your wallet's information with the `getwalletinfo` RP:

```py
wallet_info = rpc_client.getwalletinfo()
print("---------------------------------------------------------------")
print("Wallet Info:")
print("-----------")
pprint(wallet_info)
print("---------------------------------------------------------------\n")
```

You should have an output similar to the following with `logging` disabled:

```sh
---------------------------------------------------------------
Wallet Info:
-----------
{'avoid_reuse': False,
 'balance': Decimal('0.07160443'),
 'hdseedid': '6dko666b1cc0d69b7eb0539l89eba7b6390kdj02',
 'immature_balance': Decimal('0E-8'),
 'keypoololdest': 1542245729,
 'keypoolsize': 999,
 'keypoolsize_hd_internal': 1000,
 'paytxfee': Decimal('0E-8'),
 'private_keys_enabled': True,
 'scanning': False,
 'txcount': 9,
 'unconfirmed_balance': Decimal('0E-8'),
 'walletname': '',
 'walletversion': 169900}
---------------------------------------------------------------
```
Other informational commands such as `getblockchaininfo`, `getnetworkinfo`, `getpeerinfo`, and `getblockchaininfo` will work similarly.

Other commands can give you specific information on select elements within your wallet.

### Retrieving an Array

The `listtransactions` RPC allows you to look at the most recent 10 transactions on your system (or some arbitrary set of transactions using the `count` and `skip` arguments). It shows how an RPC command can return an easy-to-manipulate array:

```py
tx_list = rpc_client.listtransactions()
pprint(tx_list)
```

### Exploring a UTXO

You can similarly use `listunspent` to get an array of UTXOs on your system:

```py
print("Exploring UTXOs")
## List UTXOs
utxos = rpc_client.listunspent()
print("Utxos: ")
print("-----")
pprint(utxos)
print("------------------------------------------\n")
```

In order to manipulate an array like the one returned from `listtransactions` or `listunpsent`, you just grab the appropriate item from the appropriate element of the array:
```
## Select a UTXO - first one selected here
utxo_txid = utxos[0]['txid']
```

For `listunspent`, you get a `txid`. You can retrieve information about it with `gettransaction`, then decode that with `decoderawtransaction`:

```
utxo_hex = rpc_client.gettransaction(utxo_txid)['hex']

utxo_tx_details = rpc_client.decoderawtransaction(utxo_hex)

print("Details of Utxo with txid:", utxo_txid)
print("---------------------------------------------------------------")
print("UTXO Details:")
print("------------")
pprint(utxo_tx_details)
print("---------------------------------------------------------------\n")
```

This code is available at [walletinfo.py](src/17_4_walletinfo.py).

```
$ python3 walletinfo.py 
---------------------------------------------------------------
Wallet Info:
-----------
{'avoid_reuse': False,
 'balance': Decimal('0.01031734'),
 'hdseedid': 'da5a1b058deb9e51ecffef1b0ddc069a5dfb2c5f',
 'immature_balance': Decimal('0E-8'),
 'keypoololdest': 1596567843,
 'keypoolsize': 1000,
 'keypoolsize_hd_internal': 999,
 'paytxfee': Decimal('0E-8'),
 'private_keys_enabled': True,
 'scanning': False,
 'txcount': 6,
 'unconfirmed_balance': Decimal('0E-8'),
 'walletname': '',
 'walletversion': 169900}
---------------------------------------------------------------

Utxos: 
-----
[{'address': 'mv9cjEnS2o1EygBMdrz99LzhM8KeEMoXDg',
  'amount': Decimal('0.00001000'),
  'confirmations': 1180,
  'desc': "pkh([ce0c7e14/0'/0'/25']02d0541b9211aecd25913f7fdecfc1b469215fa326d52067b1b3f7efbd12316472)#n06pq9q5",
  'label': '-addresstype',
  'safe': True,
  'scriptPubKey': '76a914a080d1a10f5e7a02d0a291f118982ed19e8cfcd788ac',
  'solvable': True,
  'spendable': True,
  'txid': '84207ffec658ae29ad1fdd330d8a13613303c3cf281ce628fadeb7636ffb535e',
  'vout': 0},
 {'address': 'tb1qrcf8c29966tvqxhwrtd2se3rj6jeqtll3r46a4',
  'amount': Decimal('0.01029734'),
  'confirmations': 1180,
  'desc': "wpkh([ce0c7e14/0'/1'/26']02c581259ba7e6aef6d7ea23adb08f7c7f10c4c678f2e097a4074639e7685d4805)#j3pctfhf",
  'safe': True,
  'scriptPubKey': '00141e127c28a5d696c01aee1adaa8662396a5902fff',
  'solvable': True,
  'spendable': True,
  'txid': '84207ffec658ae29ad1fdd330d8a13613303c3cf281ce628fadeb7636ffb535e',
  'vout': 1},
 {'address': 'mzDxbtYY3LBBBJ6HhaBAtnHv6c51BRBTLE',
  'amount': Decimal('0.00001000'),
  'confirmations': 1181,
  'desc': "pkh([ce0c7e14/0'/0'/23']0377bdd176f985b4af2f6bdbb22c2925b6007b6c07ba171f75e65990c002615e98)#3y6ef6vu",
  'label': '-addresstype',
  'safe': True,
  'scriptPubKey': '76a914cd339342b06042bb986a45e73d56db46acc1e01488ac',
  'solvable': True,
  'spendable': True,
  'txid': '1679bee019c61608340b79810377be2798efd4d2ec3ace0f00a1967af70666b9',
  'vout': 1}]
------------------------------------------

Details of Utxo with txid: 84207ffec658ae29ad1fdd330d8a13613303c3cf281ce628fadeb7636ffb535e
---------------------------------------------------------------
UTXO Details:
------------
{'hash': '0c6c27f58f122329bbc53a91f290b35ce23bd2708706b21a04cdc387dc8e2fd9',
 'locktime': 1831103,
 'size': 225,
 'txid': '84207ffec658ae29ad1fdd330d8a13613303c3cf281ce628fadeb7636ffb535e',
 'version': 2,
 'vin': [{'scriptSig': {'asm': '', 'hex': ''},
          'sequence': 4294967294,
          'txid': '1679bee019c61608340b79810377be2798efd4d2ec3ace0f00a1967af70666b9',
          'txinwitness': ['3044022014b3e2359fb46d8cbc4cd30fa991b455edfa4b419a4c64a53fcdfc79e3ca89db022010cefc3268bc252d55f1982c426328b709b47d02332def9e2efb3b12de2cf0d301',
                          '0351b470e87b44e8e9607acf09b8d4543c51c93c17dc741176319e60202091f2be'],
          'vout': 0}],
 'vout': [{'n': 0,
           'scriptPubKey': {'addresses': ['mv9cjEnS2o1EygBMdrz99LzhM8KeEMoXDg'],
                            'asm': 'OP_DUP OP_HASH160 '
                                   'a080d1a10f5e7a02d0a291f118982ed19e8cfcd7 '
                                   'OP_EQUALVERIFY OP_CHECKSIG',
                            'hex': '76a914a080d1a10f5e7a02d0a291f118982ed19e8cfcd788ac',
                            'reqSigs': 1,
                            'type': 'pubkeyhash'},
           'value': Decimal('0.00001000')},
          {'n': 1,
           'scriptPubKey': {'addresses': ['tb1qrcf8c29966tvqxhwrtd2se3rj6jeqtll3r46a4'],
                            'asm': '0 1e127c28a5d696c01aee1adaa8662396a5902fff',
                            'hex': '00141e127c28a5d696c01aee1adaa8662396a5902fff',
                            'reqSigs': 1,
                            'type': 'witness_v0_keyhash'},
           'value': Decimal('0.01029734')}],
 'vsize': 144,
 'weight': 573}
---------------------------------------------------------------
```

## Sending Transactions

Now that we have established comfort between our python and bitcoind interface, lets create and broadcast a transaction. For the purposes of this course, we will send test bitcoins to an address generated by us in our testnet wallet. Here's how we will do it:

1. Create 2 addresses, one that will act as recipient and the other for change.
2. Select a UTXO and set transaction details.
3. Create a raw transaction.
4. Sign the raw transaction with private key of the UTXO.
5. Broadcast the transaction on the bitcoin testnet.

### 1. Create New Addresses

For the purposes of learning, we will send bitcoins to an address generated by our node. We also generate a change address to receive back change from the difference between input and recipient amounts (less the miner fees). For this we use `getrawchangeaddress`.  It's largely the same as `getnewaddress` but is optimized for use as a change address in a raw transaction, so it doesn't do things like make entries in your address book.

```py
print("Creating a Transaction")
## Create New Addresses
new_address = rpc_client.getnewaddress("Learning-Bitcoin-from-the-Command-Line")
new_change_address = rpc_client.getrawchangeaddress()
```

### 2. Select UTXO & Set Transaction Details

In the folowing code snippet we first select the UTXO which we want to spend. Then we get its address, transaction id, and the vector index of the output. Finally, we add the recipient address to which we want to send the bitcoins, enter the amount of bitcoins we want to send, set the miner fee, and calculate the change amount.

```py
selected_utxo = utxos[0]  # we select the first utxo here
utxo_address = selected_utxo['address']
utxo_txid = selected_utxo['txid']
utxo_vout = selected_utxo['vout']
utxo_amt = float(selected_utxo['amount'])
# here we are sending bitcoins to an address generated by us in our own wallet.
recipient_address = new_address
recipient_amt = utxo_amt / 2  # sending half coins to recipient
miner_fee = 0.00000200        # choose appropriate fee based on your tx size
change_address = new_change_address
change_amt = float('%.8f'%((utxo_amt - recipient_amt) - miner_fee))
print("---------------------------------------------------------------")
print("Transaction Details:")
print("-------------------")
print("UTXO Address.......: ", utxo_address)
print("UTXO Txid..........: ", utxo_txid)
print("Vector ID of Output: ", utxo_vout)
print("UTXO Amount........: ", utxo_amt)
print("Tx Amount..........: ", recipient_amt)
print("Recipient Address..: ", recipient_address)
print("Change Address.....: ", change_address)
print("Miner Fee..........: ", miner_fee)
print("Change Amount......: ", change_amt)
print("---------------------------------------------------------------\n")
```

Your output will be similar to the following:

```sh
---------------------------------------------------------------
Transaction Details:
-------------------
UTXO Address.......:  2NHkixaDUBQ8qz7oV3obwWbYXeRzsJwYTg
UTXO Txid..........:  b90sl97lfc2bfc0f16761fd1bb5f27f86e88eab440f5578fefe47143b5e4232b
Vector ID of Output:  1
UTXO Amount........:  0.01
Tx Amount..........:  0.005
Recipient Address..:  2NOLScQAYV3QH21my3kXrmn1ykTnTWXBPZ6
Change Address.....:  2NABxEDoVs85b9owihT8HGNFSnPPJTDVsFC
Miner Fee..........:  0.000002
Change Amount......:  0.004998
---------------------------------------------------------------
```

### 3. Create Raw Transacion

Now we have all the information to send a transaction, but before we can send one, we have to create a transaction. We do that by creating a raw transaction, like so:

```py
txids_vouts = [{"txid": utxo_txid, "vout": utxo_vout}]
addresses_amts = {f"{recipient_address}": recipient_amt, f"{change_address}": change_amt}
create_raw_tx = rpc_client.createrawtransaction(txids_vouts, addresses_amts)
unsigned_tx_hex = create_raw_tx
print("---------------------------------------------------------------")
print("Unsigned Transaction Hex: ", unsigned_tx_hex)
print("---------------------------------------------------------------\n")
```

This will return the hex of the raw transaction:

```sh
---------------------------------------------------------------
Unsigned Transaction Hex:  02000000012b23e4b54371e4ef8f57f540b4ea88slk8275fbbd11f76160ffc2bfc10da18b80100000000ffffffff0220a107000000000017a914e573193a39esl9ld930127551fcef86aaa47f82f8758a007000000000017a914ls90d0497b0fef38642f64ba0c8148adf0fb1d0c8700000000
---------------------------------------------------------------
```

The format of the `createrawtransaction` command is:

`$ bitcoin-cli createrawtransaction '[{"txid": <utxo_txid>, "vout": <vector_id>}]' '{"<address>": <amount>}'`

The `txids_vouts` is a list and `addresses_amts` is a python dictionary to match with the format of `createrawtransaction`.

Try checking the details of the transaction, hint: use `decoderawtransaction`.

### 4. Sign Raw Transaction

Now that we have a raw transaction, we use its hex and the private key of the UTXOs we are spending, in order to sign the transaction like so:

```py
address_priv_key = []  # list of priv keys of each utxo
address_priv_key.append(rpc_client.dumpprivkey(utxo_address))
signed_tx = rpc_client.signrawtransactionwithkey(unsigned_tx_hex, address_priv_key)
print("---------------------------------------------------------------")
print("Signed Transaction: ")
print("----------------------")
pprint(signed_tx)
print("---------------------------------------------------------------\n")
```
This returns a JSON object with the signed transaction's hex, and whether it was signed completely or not:

```sh
---------------------------------------------------------------
Signed Transaction:
----------------------
{'complete': True,
 'hex': '020000000001012b23e4b5438904ef8f57f540b4ea886ef8275fbbd11f76160ffc2bfc10da18b80100000017160014c5d04b36b7b45eb9c5e4716272e3c955a6041fc2ffffffff0220a107000000000017a914e573193a39ed74dd930127551fcef86aaa47f82f8758a007000000000017a914e7d0osl97b0fef38642f64ba0c8148adf0fb1d0c8702463043021f4e2855813369bbf08288fa8bc670a48c1b27873646296c5cdabd50ee7790810220516f03c20a72f8985fd3bd5549dkfc68993909c28ffeffb5d277456f65384e60012103fa812ff869d1839e1b1d5c9532413b0ls2dcd21c334e727d9ee221c7a151591a400000000'}
---------------------------------------------------------------
```

### Broadcast Transaction

Finally, we are now ready to broadcast our signed transaction on the bitcoin network like so:

```py
send_tx = rpc_client.sendrawtransaction(signed_tx['hex'])
print("---------------------------------------------------------------")
print("TXID of sent transaction: ", send_tx)
print("---------------------------------------------------------------\n")
```

Once the transaction has been broadcasted, bitcoind will return its TXID:

```sh
---------------------------------------------------------------
TXID of sent transaction: 'k9db702lsd512e2421915dc53clkj28f39a987c9a91cc0514faacfef500c6764'
---------------------------------------------------------------
```

## Summary

In this chapter we learned how to connect to a node, get some basic information about our node, and even sent a transaction over testnet. 

Accessing Bitcoind with Python is very easy while using the `python-bitcoinrpc` library. The first thing to always do is to establish connection with your bitcoind instance, then you can basically call all the bitcoin API calls as described in the bitcoin-core documentation. This makes it really easy to create small or large scripts to manage your own node, check balances, or create cool applications on top as you get the full power of `bitcoin-cli`.

All the source code for this chapter is available in the [src](./src/18_4_accessing_bitcoind_with_python.py) directory of the repo.

## What's Next?

[...]

## Synopsis: Building Python from Source

If you need to install Python 3 from source, follow these instructions, then continue with ["Creating a BitcoinRPC Project"](17_4_Accessing_Bitcoind_with_Python.md#creating-a-bitcoinrpc-project).

### 1. Install Dependencies
```sh
$ sudo apt-get install build-essential checkinstall
$ sudo apt-get install libreadline-gplv2-dev libncursesw5-dev libssl-dev libsqlite3-dev tk-dev libgdbm-dev libc6-dev libbz2-dev libffi-dev zlib1g-dev
```

### 2. Download & Extract Python
```sh
$ wget https://www.python.org/ftp/python/3.8.3/Python-3.8.3.tgz
$ tar -xzf Python-3.8.3.tgz
```

### 3. Compile Python Source & Check Installation:
```sh
$ cd Python-3.8.3
$ sudo ./configure --enable-optimizations
$ sudo make -j 8  # enter the number of cores of your system you want to use to speed up the build process.
$ sudo make altinstall
$ python3.8 --version
```

After you get the version output, remove the source file:

```sh
$ rm Python-3.8.3.tgz
```