Custom Python VOUT Analyzer
Custom Python VOUT Analyzer
In this final simulation, we will write a script that analyzes the Outputs of a transaction to determine their VOUT indexes. This will help you visualize exactly how a transaction creates the "OutPoints" that future transactions will spend.
The Python Output Mapper
import struct
def map_transaction_outputs(tx_hex):
# Convert hex string to raw bytes
tx_bytes = bytes.fromhex(tx_hex)
# In a real parser, we would skip the Version and Inputs
# For this simulation, we will jump directly to the Output section
# Mock data: 1 byte for output count, followed by outputs
output_count = tx_bytes[0]
cursor = 1
print(f"--- Mapping {output_count} Transaction Outputs ---")
for vout in range(output_count):
# 1. Read Value (8 bytes, Little-Endian Satoshis)
raw_value = tx_bytes[cursor:cursor+8]
satoshis = struct.unpack('<q', raw_value)[0]
cursor += 8
# 2. Read Script Length (simplified 1-byte VarInt)
script_len = tx_bytes[cursor]
cursor += 1
# 3. Read Script (for display)
script = tx_bytes[cursor:cursor+script_len].hex()
cursor += script_len
# Print the mapping
print(f"\n[VOUT {vout}]")
print(f"[*] Amount: {satoshis / 100_000_000:.8f} BTC")
print(f"[*] Script: {script}")
# --- Simulation ---
# A mock output section hex:
# [02] -> Count (2)
# [00e1f50500000000] -> 100,000,000 sats (1 BTC)
# [02] -> Script Len (2)
# [6a6a] -> Script (OP_RETURN OP_RETURN)
# [80f0fa0200000000] -> 50,000,000 sats (0.5 BTC)
# [01] -> Script Len (1)
# [6a] -> Script (OP_RETURN)
mock_output_data = "0200e1f50500000000026a6a80f0fa0200000000016a"
map_transaction_outputs(mock_output_data)
How to Run the Analyzer
-
Ensure you have Python 3 installed.
-
Copy the code into a file named
vout_analyzer.py. -
Run it using
python3 vout_analyzer.py.
Technical Takeaways
-
Zero-Based Indexing: Notice how the
range(output_count)naturally assigns 0 to the first output. This is exactly how Bitcoin Core handles it. -
Implicit Indexing: The VOUT is never actually written into the output section of a transaction. It is implied by the order in which the outputs appear.
-
OutPoint Genesis: By knowing the order of these outputs, you can predict the exact OutPoint that will be used in the future to spend them.
Congratulations! You have completed the VOUT & Output Indexing module. You now understand the coordinate system of the world's most secure ledger.
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