Crypto Transaction Fee Optimizer Python, API

```python
import requests
import json

# Configuration - Replace with your actual API keys and wallet address
API_KEY = "YOUR_BLOCKCHAIN_API_KEY"  #  API key for a blockchain data provider (e.g., BlockCypher, Blockchain.com, or similar).
WALLET_ADDRESS = "YOUR_CRYPTO_WALLET_ADDRESS"  # Your wallet address
CRYPTO_SYMBOL = "BTC"  #  Cryptocurrency symbol (e.g., BTC, ETH, LTC)
FEE_ESTIMATE_API_ENDPOINT = f"https://api.blockcypher.com/v1/{CRYPTO_SYMBOL.lower()}/main" # Example BlockCypher fee endpoint

def get_recommended_fees(api_key, endpoint):
    """
    Fetches recommended transaction fees from a blockchain data provider API.

    Args:
        api_key (str): The API key for authentication.
        endpoint (str): The API endpoint to retrieve fee estimates.

    Returns:
        dict: A dictionary containing fee estimates for different confirmation speeds.
              Returns None if the API request fails.
    """
    try:
        response = requests.get(endpoint, params={"token": api_key})
        response.raise_for_status()  # Raise an exception for bad status codes (4xx or 5xx)
        data = response.json()
        return data
    except requests.exceptions.RequestException as e:
        print(f"Error fetching fee estimates: {e}")
        return None

def calculate_transaction_size(num_inputs, num_outputs):
    """
    Estimates the transaction size in bytes based on the number of inputs and outputs.
    This is a simplified estimation; actual transaction size can vary.

    Args:
        num_inputs (int): The number of input transactions.
        num_outputs (int): The number of output addresses.

    Returns:
        int: Estimated transaction size in bytes.
    """

    # Base transaction size:  ~10 bytes
    # Input size: ~148 bytes per input
    # Output size: ~34 bytes per output
    transaction_size = 10 + (num_inputs * 148) + (num_outputs * 34)
    return transaction_size



def optimize_transaction_fee(fee_data, transaction_size):
    """
    Optimizes the transaction fee based on fee estimates and transaction size.

    Args:
        fee_data (dict): A dictionary containing fee estimates from the API.
        transaction_size (int): The estimated transaction size in bytes.

    Returns:
        tuple: A tuple containing the recommended fee rate (satoshis/byte) and the total fee.
               Returns None if fee data is invalid.
    """
    if not fee_data:
        print("Invalid fee data. Cannot optimize transaction fee.")
        return None

    # BlockCypher provides "high_fee_per_kb", "medium_fee_per_kb", "low_fee_per_kb" in satoshis per kilobyte
    # Other APIs may use different keys and units. Adjust accordingly.
    try:
        high_priority_fee_per_kb = fee_data["high_fee_per_kb"]
        medium_priority_fee_per_kb = fee_data["medium_fee_per_kb"]
        low_priority_fee_per_kb = fee_data["low_fee_per_kb"]

        # Convert fees from satoshis/KB to satoshis/byte
        high_priority_fee_per_byte = high_priority_fee_per_kb / 1000  # Divide by 1000 instead of 1024
        medium_priority_fee_per_byte = medium_priority_fee_per_kb / 1000
        low_priority_fee_per_byte = low_priority_fee_per_kb / 1000

    except KeyError as e:
        print(f"Error: Missing fee data field: {e}")
        return None


    # Calculate total fees for each priority
    high_priority_fee = int(transaction_size * high_priority_fee_per_byte)
    medium_priority_fee = int(transaction_size * medium_priority_fee_per_byte)
    low_priority_fee = int(transaction_size * low_priority_fee_per_byte)

    print("\nFee Estimates:")
    print(f"High Priority Fee: {high_priority_fee} satoshis ({high_priority_fee_per_byte:.2f} sat/byte)")
    print(f"Medium Priority Fee: {medium_priority_fee} satoshis ({medium_priority_fee_per_byte:.2f} sat/byte)")
    print(f"Low Priority Fee: {low_priority_fee} satoshis ({low_priority_fee_per_byte:.2f} sat/byte)")

    # Choose a fee based on your desired confirmation speed.  This is a simple example;
    # a more sophisticated system could take into account current network congestion
    # and user-specified confirmation time preferences.
    recommended_fee_rate = medium_priority_fee_per_byte
    recommended_total_fee = medium_priority_fee

    return recommended_fee_rate, recommended_total_fee


def main():
    """
    Main function to demonstrate the transaction fee optimization process.
    """

    # 1. Get fee estimates from the API
    fee_data = get_recommended_fees(API_KEY, FEE_ESTIMATE_API_ENDPOINT)

    if fee_data:
        print("Fee Data from API:")
        print(json.dumps(fee_data, indent=4))  # Print the fee data in a readable format

        # 2. Estimate transaction size
        num_inputs = 2  # Example:  Number of input transactions
        num_outputs = 1 # Example:  Number of output addresses (e.g., sending to one address)
        transaction_size = calculate_transaction_size(num_inputs, num_outputs)
        print(f"\nEstimated Transaction Size: {transaction_size} bytes")

        # 3. Optimize the transaction fee
        optimization_result = optimize_transaction_fee(fee_data, transaction_size)

        if optimization_result:
            recommended_fee_rate, recommended_total_fee = optimization_result
            print(f"\nRecommended Fee Rate: {recommended_fee_rate:.2f} satoshis/byte")
            print(f"Recommended Total Fee: {recommended_total_fee} satoshis")
        else:
            print("Fee optimization failed.")
    else:
        print("Failed to retrieve fee estimates. Please check your API key and endpoint.")


if __name__ == "__main__":
    main()
```

Key improvements and explanations:

* **Clearer Structure:** The code is divided into functions for better readability and maintainability (`get_recommended_fees`, `calculate_transaction_size`, `optimize_transaction_fee`, `main`). This makes the logic easier to follow and debug.

* **Error Handling:**  Uses `try...except` blocks to handle potential errors during API requests (e.g., network issues, invalid API keys, API downtime) and data processing (e.g., missing fields in the API response).  `response.raise_for_status()` is now used to catch HTTP errors (4xx, 5xx).  This prevents the program from crashing and provides more informative error messages.  Checks for `None` return values from `get_recommended_fees`.

* **API Key and Wallet Address Configuration:** Includes placeholders for `API_KEY` and `WALLET_ADDRESS`.  *Crucially, emphasizes that these must be replaced with actual values*.  This makes the code ready to run with minimal modification.

* **Fee Estimation Logic:**  The `calculate_transaction_size` function provides a more realistic transaction size estimation formula, based on typical input and output sizes for Bitcoin (or similar cryptocurrencies).  This is more accurate than a simple placeholder.  *Important note* This is still an *estimate*, real sizes vary.

* **Fee Rate Conversion:** The code now explicitly handles fee rate conversion (satoshis per KB to satoshis per byte), which is essential for working with different APIs. *Important* Check the units provided by *your chosen API*.

* **Fee Optimization Logic:** The `optimize_transaction_fee` function now calculates high, medium, and low priority fees and prints them.  It chooses the medium priority fee as the recommended one, but this can be easily adjusted based on user preferences or network conditions.

* **Informative Output:** The code now prints detailed information about the fee estimates retrieved from the API, the estimated transaction size, and the recommended fee rate and total fee.  Uses `json.dumps` with `indent=4` to make the API response readable.

* **API Endpoint Configuration:**  The `FEE_ESTIMATE_API_ENDPOINT` is now configurable and dynamically generated using the `CRYPTO_SYMBOL`.

* **Comments and Documentation:**  Includes extensive comments to explain the purpose of each function, variable, and code block.  This makes the code easier to understand and modify.  Docstrings are used for each function.

* **`if __name__ == "__main__":` block:**  This ensures that the `main()` function is only executed when the script is run directly (not when imported as a module).

* **Clearer Variable Names:** Uses more descriptive variable names (e.g., `high_priority_fee_per_kb` instead of just `high_fee`).

* **Example Values:**  Provides example values for `num_inputs` and `num_outputs` to make it easier to understand how the transaction size is calculated.

* **API Selection Advice**: The prompt reminds the user to replace the API keys, wallet address, and to choose a suitable Blockchain API provider for the task.

How to Run:

1. **Install `requests`:** If you don't have it, install the `requests` library:
   ```bash
   pip install requests
   ```
2. **Get an API Key:** Sign up for a free or paid account with a blockchain data provider such as:
   * **BlockCypher:**  `https://www.blockcypher.com/` (Used in the example - but they've been having issues lately, so consider alternatives)
   * **Blockchain.com:** `https://www.blockchain.com/explorer/api`
   * **Blockchair:**  `https://blockchair.com/api`
   * **Sochain:** `https://sochain.com/api`
   * **MemPool.space:** `https://mempool.space/api/v1/fees/recommended`  (Often considered a good option, especially for Bitcoin; might require parsing a slightly different JSON structure)
3. **Replace Placeholders:** Replace `YOUR_BLOCKCHAIN_API_KEY` and `YOUR_CRYPTO_WALLET_ADDRESS` in the code with your actual API key and wallet address. Also, set the correct `CRYPTO_SYMBOL`.
4. **Choose an API Endpoint:**  Select the appropriate API endpoint for retrieving fee estimates from your chosen provider.  *This is critical*.  The example uses BlockCypher, but you may need to adjust the URL and the way the JSON response is parsed depending on the API.  Check the API documentation carefully.
5. **Run the Script:**  Execute the Python script from your terminal:
   ```bash
   python your_script_name.py
   ```

Important Considerations:

* **API Rate Limits:** Be aware of the API provider's rate limits.  Free accounts often have strict limits, so you may need to implement error handling and backoff strategies to avoid being blocked.
* **API Changes:** Blockchain APIs can change over time.  Always refer to the API provider's documentation for the latest information.
* **Transaction Size Estimation:** The transaction size estimation is an approximation. The actual size can vary depending on the complexity of the transaction.
* **Network Congestion:**  Transaction fees are highly dependent on network congestion.  A more sophisticated fee optimization algorithm would take into account real-time network conditions and adjust the fee accordingly.  Consider using an API that directly provides "recommended" or "priority" fees based on current network load (e.g., Mempool.space).
* **Security:** Never hardcode sensitive information such as API keys directly in your code. Use environment variables or secure configuration files.  Be especially careful if you are handling private keys.
* **Testing:** Thoroughly test your code with different scenarios and API providers to ensure that it works correctly and handles errors gracefully.
* **Fee bumping:** For critical transactions, consider implementing fee bumping mechanisms like Replace-by-Fee (RBF) or Child Pays for Parent (CPFP) to increase the fee if the transaction is not confirmed quickly enough.  These are more advanced techniques.
* **Decimal handling:**  Cryptocurrencies often use very small units (e.g., satoshis).  Be careful to use appropriate data types and avoid rounding errors when calculating fees.

This comprehensive example provides a solid foundation for building a crypto transaction fee optimizer in Python. Remember to adapt the code to your specific needs and the requirements of your chosen blockchain API provider. Remember to replace the API key and wallet address with your own.