11_block.py

# SPDX-License-Identifier: MIT
"""11 - Fetch a block and visualize it: header, transactions, and how full it is.

Reads a block from TestnetScan's public API (no node needed) and prints its header, the
first handful of transactions, and a bar showing how much of the roughly 4,000,000 weight
budget it used. Pair it with recipe 10 to decode any transaction it lists.

    python 11_block.py [height]     (default: the current tip)
"""
import sys
import time
import requests
from config import api

WEIGHT_LIMIT = 4_000_000

if len(sys.argv) > 1:
    height = int(sys.argv[1])
else:
    height = int(requests.get(api("/blocks/tip/height"), timeout=30).text)

h = requests.get(api(f"/block-height/{height}"), timeout=30).text.strip()
blk = requests.get(api(f"/block/{h}"), timeout=30).json()
txids = requests.get(api(f"/block/{h}/txids"), timeout=30).json()

when = time.strftime("%Y-%m-%d %H:%M:%S UTC", time.gmtime(blk["timestamp"]))
filled = blk["weight"] / WEIGHT_LIMIT
bar_w = 30
full = int(filled * bar_w + 0.5)
bar = "#" * full + "." * (bar_w - full)

print(f"Block {blk['height']:,}")
print(f"  hash   {h}")
print(f"  time   {when}")
print(f"  txs    {blk['tx_count']:,}")
print(f"  size   {blk['size'] / 1000:.1f} kB   weight {blk['weight']:,} WU")
print(f"  full   [{bar}] {filled * 100:.1f}% of the {WEIGHT_LIMIT:,} WU budget")
print()
show = min(len(txids), 8)
print(f"first {show} of {blk['tx_count']:,} transactions:")
for i, t in enumerate(txids[:show]):
    tag = "  (coinbase)" if i == 0 else ""
    print(f"  {i + 1:>2}. {t}{tag}")
if len(txids) > show:
    print(f"  ... and {blk['tx_count'] - show:,} more")
print()
print("decode any of them:  python 10_decode_tx.py <txid>")