Update pow_algorithm.py

Author: anurags10

blockchain/pow_algorithm.py

@@ -1,25 +1,22 @@
-"""
 # Title: Proof of Work Algorithm for Blockchain
 
 ## Algorithm Statement:
-The algorithm implements the Proof of Work (PoW) consensus mechanism used in
-blockchain to validate blocks. PoW ensures participants (miners) perform a
-computational task to create a valid block and add it to the blockchain. The
-difficulty is defined by the number of leading zeros required in the block hash.
-"""
+# The algorithm implements the Proof of Work (PoW) consensus mechanism used in
+# blockchain to validate blocks. PoW ensures participants (miners) perform a
+# computational task to create a valid block and add it to the blockchain. The
+# difficulty is defined by the number of leading zeros required in the block hash.
 
 import hashlib
 import time
 
-
 class Block:
     def __init__(
         self,
         index: int,
         previous_hash: str,
         transactions: str,
         timestamp: float,
-        difficulty: int,
+        difficulty: int
     ) -> None:
         """
         Initializes a Block object with the specified parameters.
@@ -28,7 +25,8 @@ def __init__(
         - index (int): The index of the block in the blockchain.
         - previous_hash (str): The hash of the previous block.
         - transactions (str): The list of transactions in the block.
-        - timestamp (float): The time when the block was created (in Unix timestamp format).
+        - timestamp (float): The time when the block was created
+          (in Unix timestamp format).
         - difficulty (int): The difficulty level for mining this block.
         """
         self.index = index
@@ -42,9 +40,9 @@ def __init__(
     def compute_hash(self) -> str:
         """
         Generates the hash of the block content.
-        Combines index, previous hash, transactions, timestamp, and nonce into a string,
-        which is then hashed using SHA-256.
-
+        Combines index, previous hash, transactions, timestamp, and nonce into
+        a string, which is then hashed using SHA-256.
+        
         Returns:
         - str: The hash of the block.
         """
@@ -57,40 +55,38 @@ def compute_hash(self) -> str:
     def mine_block(self) -> None:
         """
         Performs Proof of Work by adjusting the nonce until a valid hash is found.
-        A valid hash has the required number of leading zeros based on the difficulty level.
-
+        A valid hash has the required number of leading zeros based on the
+        difficulty level.
+        
         Returns:
         - None
         """
-        target = (
-            "0" * self.difficulty
-        )  # Target hash should start with 'difficulty' zeros
-        while self.hash[: self.difficulty] != target:
+        target = '0' * self.difficulty  # Target hash should start with 'difficulty' zeros
+        while self.hash[:self.difficulty] != target:
             self.nonce += 1
             self.hash = self.compute_hash()
 
         print(f"Block mined with nonce {self.nonce}, hash: {self.hash}")
 
-
 class Blockchain:
     def __init__(self, difficulty: int) -> None:
         """
         Initializes the blockchain with a given difficulty level.
 
         Parameters:
         - difficulty (int): The difficulty level for mining blocks in this blockchain.
-
+        
         Returns:
         - None
         """
-        self.chain = []
+        self.chain: list[Block] = []  # Adding type hint for the list of blocks
         self.difficulty = difficulty
         self.create_genesis_block()
 
     def create_genesis_block(self) -> None:
         """
         Creates the first block in the blockchain (the Genesis block).
-
+        
         Returns:
         - None
         """
@@ -104,24 +100,21 @@ def add_block(self, transactions: str) -> None:
 
         Parameters:
         - transactions (str): The list of transactions to be added in the new block.
-
+        
         Returns:
         - None
         """
         previous_block = self.chain[-1]
         new_block = Block(
-            len(self.chain),
-            previous_block.hash,
-            transactions,
-            time.time(),
-            self.difficulty,
+            len(self.chain), previous_block.hash, transactions, time.time(), 
+            self.difficulty
         )
         new_block.mine_block()
         self.chain.append(new_block)
 
     def is_chain_valid(self) -> bool:
         """
-        Verifies the integrity of the blockchain by ensuring each block's previous
+        Verifies the integrity of the blockchain by ensuring each block's previous 
         hash matches and that all blocks meet the Proof of Work requirement.
 
         Returns:
@@ -141,37 +134,42 @@ def is_chain_valid(self) -> bool:
 
         return True
 
-
 # Test cases
 
-
+## Test Case 1: Blockchain Initialization and Genesis Block
+# This test verifies if the blockchain is correctly initialized with a Genesis block
+# and if the block is successfully mined.
 def test_blockchain() -> None:
     """
     Test cases for the Blockchain proof of work algorithm.
-
+    
     Returns:
     - None
     """
     # Create blockchain with difficulty level of 4 (hash should start with 4 zeros)
     blockchain = Blockchain(difficulty=4)
 
-    # Add new blocks
+    ## Test Case 2: Add a block and verify the block is mined
+    # This test adds a new block with transactions and ensures it's mined according
+    # to the proof of work mechanism.
     blockchain.add_block("Transaction 1: Alice pays Bob 5 BTC")
     blockchain.add_block("Transaction 2: Bob pays Charlie 3 BTC")
 
-    # Verify the integrity of the blockchain
+    ## Test Case 3: Verify blockchain integrity
+    # This test checks that the blockchain remains valid after adding new blocks
     assert blockchain.is_chain_valid(), "Blockchain should be valid"
 
-    # Tamper with the blockchain and check validation
-    blockchain.chain[
-        1
-    ].transactions = "Transaction 1: Alice pays Bob 50 BTC"  # Tampering
-    assert (
-        not blockchain.is_chain_valid()
-    ), "Blockchain should be invalid due to tampering"
+    ## Test Case 4: Tampering with the blockchain
+    # This test simulates tampering with the blockchain and checks that the validation
+    # correctly detects the tampering.
+    blockchain.chain[1].transactions = "Transaction 1: Alice pays Bob 50 BTC"  # Tampering
+    assert not blockchain.is_chain_valid(), "Blockchain should be invalid due to tampering"
 
+    ## Test Case 5: Correct blockchain validation
+    # This test checks if the blockchain becomes invalid after tampering and verifies
+    # if the PoW still holds after tampering is done.
+    
     print("All test cases passed.")
 
-
 if __name__ == "__main__":
     test_blockchain()