Bitcoin Price Index

Bitcoin logo

Bitcoin is a form of digitial currency, otherwise known as cryptocurrency. Rather than rely on a central authority like a bank, Bitcoin instead relies on a distributed network, otherwise known as a blockchain, to record transactions.

Because there’s demand for Bitcoin (i.e., users want it), users are willing to buy it, as by exchanging one currency (e.g., USD) for Bitcoin.

In a file called bitcoin.py, implement a program that:

Expects the user to specify as a command-line argument the number of Bitcoins, $n$, that they would like to buy. If that argument cannot be converted to a float, the program should exit via sys.exit with an error message.
Queries the API for the CoinDesk Bitcoin Price Index at https://api.coindesk.com/v1/bpi/currentprice.json, which returns a JSON object, among whose nested keys is the current price of Bitcoin as a float. Be sure to catch any exceptions, as with code like:
```
import requests

try:
    ...
except requests.RequestException:
    ...
```
Outputs the current cost of $n$ Bitcoins in USD to four decimal places, using , as a thousands separator.

Hints

Recall that the sys module comes with argv, per docs.python.org/3/library/sys.html#sys.argv.
Note that the requests module comes with quite a few methods, per requests.readthedocs.io/en/latest, among which are get, per requests.readthedocs.io/en/latest/user/quickstart/#make-a-request, and json, per requests.readthedocs.io/en/latest/user/quickstart/#json-response-content. You can install it with:
```
pip install requests
```

Note that CoinDesk’s API returns a JSON response like:

{
   "time":{
      "updated":"May 2, 2022 15:27:00 UTC",
      "updatedISO":"2022-05-02T15:27:00+00:00",
      "updateduk":"May 2, 2022 at 16:27 BST"
   },
   "disclaimer":"This data was produced from the CoinDesk Bitcoin Price Index (USD). Non-USD currency data converted using hourly conversion rate from openexchangerates.org",
   "chartName":"Bitcoin",
   "bpi":{
      "USD":{
         "code":"USD",
         "symbol":"&#36;",
         "rate":"38,761.0833",
         "description":"United States Dollar",
         "rate_float":38761.0833
      },
      "GBP":{
         "code":"GBP",
         "symbol":"&pound;",
         "rate":"30,827.6198",
         "description":"British Pound Sterling",
         "rate_float":30827.6198
      },
      "EUR":{
         "code":"EUR",
         "symbol":"&euro;",
         "rate":"36,800.2764",
         "description":"Euro",
         "rate_float":36800.2764
      }
   }
}

Recall that you can format USD to four decimal places with a thousands separator with code like:
```
print(f"${amount:,.4f}")
```

Demo

This demo was recorded when the price of Bitcoin was $38,761.0833. Your own output may vary.

How to Test

Here’s how to test your code manually:

Run your program with python bitcoin.py. Your program should use sys.exit to exit with an error message:
```
Missing command-line argument   
```
Run your program with python bitcoin.py cat. Your program should use sys.exit to exit with an error message:
```
Command-line argument is not a number
```
Run your program with python bitcoin.py 1. Your program should output the price of a single Bitcoin to four decimal places, using , as a thousands separator.
Run your program with python bitcoin.py 2. Your program should output the price of two Bitcoin to four decimal places, using , as a thousands separator.
Run your program with python bitcoin.py 2.5. Your program should output the price of 2.5 Bitcoin to four decimal places, using , as a thousands separator.