feat: add python tab to language bindings starter example

Author: busayo-OD

docs/cookbook/bindings/starter-example.md

@@ -16,7 +16,7 @@ So you want to build a bitcoin wallet using BDK. Great! Here is the rough outlin
 
 This page provides a starter example showcasing how BDK can be used to create, sync, and manage a wallet using an Esplora client as a blockchain data source. Familiarity with this example will help you work through the more advanced pages in this section.
 
-You can find [working code examples](https://github.com/bitcoindevkit/book-of-bdk/tree/master/examples) of this example in two programming languages: [Swift](https://github.com/bitcoindevkit/book-of-bdk/tree/master/examples/swift) and [Kotlin](https://github.com/bitcoindevkit/book-of-bdk/tree/master/examples/kotlin). (Note: some additional language bindings are available for BDK, see [3rd Party Bindings](../getting-started/3rd-party-bindings.md)).
+You can find [working code examples](https://github.com/bitcoindevkit/book-of-bdk/tree/master/examples) of this example in three programming languages: [Swift](https://github.com/bitcoindevkit/book-of-bdk/tree/master/examples/swift), [Kotlin](https://github.com/bitcoindevkit/book-of-bdk/tree/master/examples/kotlin) and [Python](https://github.com/bitcoindevkit/book-of-bdk/tree/master/examples/python). (Note: some additional language bindings are available for BDK, see [3rd Party Bindings](../getting-started/3rd-party-bindings.md)).
 
 !!!tip
     To complete this example from top to bottom, you'll need to create new descriptors and replace the ones provided. Once you do so, you'll run the example twice; on first run the wallet will not have any balance and will exit with an address to send funds to. Once that's done, you can run the example again and the wallet will be able to perform the later steps, namely creating and broadcasting a new transaction.
@@ -35,12 +35,21 @@ You can find [working code examples](https://github.com/bitcoindevkit/book-of-bd
     gradle init
     ```
 
+=== "Python"
+
+    ```shell
+    python3 -m venv venv
+    source venv/bin/activate
+    mkdir src
+    touch src/app.py requirements.txt
+    ```
+
 ## Add required dependencies
 
 === "Swift"
 
     ```toml title="Package.swift"
-    --8<-- "examples/swift/quickstart/Package.swift"
+    --8<-- "examples/swift/starter-example/Package.swift"
     ```
     Or, if you're building an iOS app:
 
@@ -63,6 +72,12 @@ You can find [working code examples](https://github.com/bitcoindevkit/book-of-bd
     }
     ```
 
+=== "Python"
+
+    ```text title="requirements.txt"
+    bdkpython==2.2.0
+    ```
+
 ## Use descriptors
 
 To create a wallet using BDK, we need some <a href="https://github.com/bitcoin/bitcoin/blob/master/doc/descriptors.md" target="_blank">descriptors</a> for our wallet. This example uses public descriptors (meaning they cannot be used to sign transactions) on Signet. Step 7 and below will fail unless you replace those public descriptors with private ones of your own and fund them using Signet coins through a faucet. Refer to the [Creating Descriptors](./keys-descriptors/descriptors.md) page for information on how to generate your own private descriptors.
@@ -82,6 +97,12 @@ To create a wallet using BDK, we need some <a href="https://github.com/bitcoin/b
     --8<-- "examples/kotlin/starter-example/app/src/main/kotlin/org/starterexample/App.kt:descriptors"
     ```
 
+=== "Python"
+    
+    ```python
+    --8<-- "examples/python/starter-example/src/app.py:descriptors"
+    ```
+
 These are taproot descriptors (`tr()`) using public keys on Signet (`tpub`) as described in <a href="https://github.com/bitcoin/bips/blob/master/bip-0086.mediawiki" target="_blank">BIP86</a>. The first descriptor is an HD wallet with a path for generating addresses to give out externally for payments. The second one is used by the wallet to generate addresses to pay ourselves change when sending payments (remember that <a href="https://github.com/bitcoinbook/bitcoinbook/blob/develop/ch06_transactions.adoc#outpoint" target="_blank">UTXOs</a> must be spent in full, so you often need to make change).
 
 ## Create or load a wallet
@@ -100,6 +121,12 @@ Next let's load up our wallet.
     --8<-- "examples/kotlin/starter-example/app/src/main/kotlin/org/starterexample/App.kt:wallet"
     ```
 
+=== "Python"
+    
+    ```python
+    --8<-- "examples/python/starter-example/src/app.py:wallet"
+    ```
+
 ## Sync the wallet
 
 Now let's build an Esplora client and use it to request transaction history for the wallet.
@@ -116,6 +143,12 @@ Now let's build an Esplora client and use it to request transaction history for
     --8<-- "examples/kotlin/starter-example/app/src/main/kotlin/org/starterexample/App.kt:client"
     ```
 
+=== "Python"
+    
+    ```python
+    --8<-- "examples/python/starter-example/src/app.py:client"
+    ```
+
 In cases where you are using new descriptors that do not have a balance yet, the example will request a new address from the wallet and print it out so you can fund the wallet. Remember that this example uses Signet coins!
 
 === "Swift"
@@ -130,6 +163,12 @@ In cases where you are using new descriptors that do not have a balance yet, the
     --8<-- "examples/kotlin/starter-example/app/src/main/kotlin/org/starterexample/App.kt:address"
     ```
 
+=== "Python"
+    
+    ```python
+    --8<-- "examples/python/starter-example/src/app.py:address"
+    ```
+
 ## Send a transaction
 
 For this step you'll need a wallet built with private keys, funded with some Signet satoshis. You can find a faucet [here](https://signet25.bublina.eu.org/) to get some coins.
@@ -148,6 +187,12 @@ Let's prepare to send a transaction. The two core choices here are where to send
     --8<-- "examples/kotlin/starter-example/app/src/main/kotlin/org/starterexample/App.kt:client"
     ```
 
+=== "Python"
+    
+    ```python
+    --8<-- "examples/python/starter-example/src/app.py:recipient"
+    ```
+
 Here we are sending 5000 sats back to the faucet (make sure the wallet has at least this much balance, or change this value).
 
 Finally we are ready to build, sign, and broadcast the transaction:
@@ -164,4 +209,10 @@ Finally we are ready to build, sign, and broadcast the transaction:
     --8<-- "examples/kotlin/starter-example/app/src/main/kotlin/org/starterexample/App.kt:transaction"
     ```
 
+=== "Python"
+    
+    ```python
+    --8<-- "examples/python/starter-example/src/app.py:transaction"
+    ```
+
 We can view our transaction on the [mempool.space Signet explorer](https://mempool.space/signet).

examples/python/starter-example/requirements.txt

@@ -0,0 +1 @@
+bdkpython==2.2.0

examples/python/starter-example/src/app.py

@@ -0,0 +1,99 @@
+import sys
+from pathlib import Path
+from bdkpython import (
+    Descriptor,
+    Network,
+    Persister,
+    Wallet,
+    EsploraClient,
+    KeychainKind,
+    Address,
+    Amount,
+    TxBuilder,
+    FeeRate,
+)
+
+SIGNET_ESPLORA_URL = "http://signet.bitcoindevkit.net"
+PERSISTENCE_FILE_PATH = str(Path.cwd() / "starter.sqlite")
+
+
+def main():
+    # --8<-- [start:descriptors]
+    descriptor = Descriptor(
+        "tr([12071a7c/86'/1'/0']tpubDCaLkqfh67Qr7ZuRrUNrCYQ54sMjHfsJ4yQSGb3aBr1yqt3yXpamRBUwnGSnyNnxQYu7rqeBiPfw3mjBcFNX4ky2vhjj9bDrGstkfUbLB9T/0/*)#z3x5097m",
+        Network.SIGNET,
+    )
+    change_descriptor = Descriptor(
+        "tr([12071a7c/86'/1'/0']tpubDCaLkqfh67Qr7ZuRrUNrCYQ54sMjHfsJ4yQSGb3aBr1yqt3yXpamRBUwnGSnyNnxQYu7rqeBiPfw3mjBcFNX4ky2vhjj9bDrGstkfUbLB9T/1/*)#n9r4jswr",
+        Network.SIGNET,
+    )
+    # --8<-- [end:descriptors]
+
+    # --8<-- [start:wallet]
+    db_path = Path(PERSISTENCE_FILE_PATH)
+    persistence_exists = db_path.exists()
+    persister = Persister.new_sqlite(PERSISTENCE_FILE_PATH)
+
+    if persistence_exists:
+        print("Loading up existing wallet")
+        wallet = Wallet.load(
+            descriptor=descriptor,
+            change_descriptor=change_descriptor,
+            persister=persister,
+        )
+    else:
+        print("Creating new wallet")
+        wallet = Wallet(
+            descriptor=descriptor,
+            change_descriptor=change_descriptor,
+            network=Network.SIGNET,
+            persister=persister,
+        )
+    # --8<-- [end:wallet]
+
+    # --8<-- [start:client]
+    esplora_client = EsploraClient(SIGNET_ESPLORA_URL)
+    full_scan_request = wallet.start_full_scan().build()
+    update = esplora_client.full_scan(
+        request=full_scan_request, stop_gap=10, parallel_requests=1
+    )
+    wallet.apply_update(update)
+    balance = wallet.balance().total.to_sat()
+    print(f"Balance: {balance}")
+    # --8<-- [end:client]
+
+    # --8<-- [start:address]
+    if balance < 5000:
+        print("Your wallet does not have sufficient balance for the following steps!")
+        address_info = wallet.reveal_next_address(KeychainKind.EXTERNAL)
+        print(
+            f"Send Signet coins to address {address_info.address} (address generated at index {address_info.index})"
+        )
+        wallet.persist(persister)
+        sys.exit(0)
+    # --8<-- [end:address]
+
+    # --8<-- [start:recipient]
+    faucet_address = Address(
+        "tb1p4tp4l6glyr2gs94neqcpr5gha7344nfyznfkc8szkreflscsdkgqsdent4", Network.SIGNET
+    )
+    amount = Amount.from_sat(4000)
+    # --8<-- [end:recipient]
+
+    # --8<-- [start:transaction]
+    psbt = (
+        TxBuilder()
+        .add_recipient(faucet_address.script_pubkey(), amount)
+        .fee_rate(FeeRate.from_sat_per_vb(7))
+        .finish(wallet)
+    )
+
+    wallet.sign(psbt)
+    tx = psbt.extract_tx()
+    esplora_client.broadcast(tx)
+    print(f"Transaction broadcast successfully! Txid: {tx.compute_txid()}")
+    # --8<-- [end:transaction]
+
+
+if __name__ == "__main__":
+    main()