Simple blockchain with simple mining similar to bitcoin

blockchain/python/Blockchain.py

@@ -0,0 +1,79 @@
+import time, hashlib, json
+
+
+"""
+Created by trustgeek on 2017-10-23 (11:04).
+"""
+
+class Block:
+    def __init__(self, index, timestamp, data, previous_hash):
+        self._index = index
+        self._timestamp = timestamp
+        self._data = data
+        self._previous_hash = previous_hash
+        self._nounce = None
+        self._hash = self.hash()
+
+    def valid_hash(self, the_hash):
+        return the_hash.startswith('0000')
+
+    def mined(self):
+        return self._nounce is not None
+
+    def mine(self):
+        start_time = time.time()
+        the_nounce = self._nounce or 0
+        while True:
+            the_hash = self.hash(nonce=the_nounce)
+            if self.valid_hash(the_hash):
+                self._hash = the_hash
+                self._nounce = the_nounce
+                end_time = time.time()
+                time_taken = end_time - start_time
+                print("----- Mine time: %s -----" % time_taken)
+                return
+            else:
+                the_nounce += 1
+
+    def hash(self, nonce=None):
+        self._nounce = nonce or self._nounce
+        block_json = {'index': self._index, 'timestamp': self._timestamp, 'data': self._data,
+                      'previous_hash': self._previous_hash, 'nounce': self._nounce}
+
+        return hashlib.sha256(json.dumps(block_json).encode('utf-8')).hexdigest()
+
+    def __str__(self):
+        return json.dumps(
+            {'index': self._index, 'timestamp': self._timestamp, 'data': self._data,
+             'previous_hash': self._previous_hash,
+             'hash': self._hash, 'nounce': self._nounce})
+
+
+# genesis block is the first block in the blockchain
+def genesis_block():
+    return Block(0, time.time(), "This is genesis block", '0')
+
+
+# create next block for blockchain
+def next_block(_previous_block, data):
+    _new_index = _previous_block._index + 1
+    _new_timestamp = time.time()
+    _previous_hash = _previous_block._hash
+    return Block(_new_index, _new_timestamp, data, _previous_hash)
+
+
+blockchain = [genesis_block()]
+
+# first block for blockchain
+previous_block = blockchain[0]
+num_of_blocks = 20
+
+# iteratively adding block to blockchain
+for i in range(0, num_of_blocks):
+    transaction = {'from': '0x12345' + str(i), 'to': '0x54321' + str(i * 3), 'amount': 100}
+    new_block = next_block(previous_block, transaction)
+    new_block.mine()
+    blockchain.append(new_block)
+    previous_block = new_block
+    print("Block added to blockchain")
+    print(new_block)