Merge branch 'code_samples' into develop

code/get-utxo.py

@@ -0,0 +1,28 @@
+# get unspent outputs from blockchain API
+
+import json
+import requests
+
+# example address
+address = '1Dorian4RoXcnBv9hnQ4Y2C1an6NJ4UrjX'
+
+# The API URL is https://blockchain.info/unspent?active=<address>
+# It returns a JSON object with a list "unspent_outputs", containing UTXO, like this:
+#{	"unspent_outputs":[
+#   {
+#     "tx_hash":"ebadfaa92f1fd29e2fe296eda702c48bd11ffd52313e986e99ddad9084062167",
+#     "tx_index":51919767,
+#     "tx_output_n": 1,
+#     "script":"76a9148c7e252f8d64b0b6e313985915110fcfefcf4a2d88ac",
+#     "value": 8000000,
+#     "value_hex": "7a1200",
+#     "confirmations":28691
+#   },
+# ...
+#]}
+
+resp = requests.get('https://blockchain.info/unspent?active=%s' % address)
+utxo_set = json.loads(resp.text)["unspent_outputs"]
+
+for utxo in utxo_set:
+    print "%s:%d - %ld Satoshis" % (utxo['tx_hash'], utxo['tx_output_n'], utxo['value'])

code/max_money.py

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+# Original block reward for miners was 50 BTC
+start_block_reward = 50
+# 210000 is around every 4 years with a 10 minute block interval
+reward_interval = 210000
+
+def max_money():
+    # 50 BTC = 50 0000 0000 Satoshis
+    current_reward = 50 * 10**8
+    total = 0
+    while current_reward > 0:
+        total += reward_interval * current_reward
+        current_reward /= 2
+    return total
+
+print "Total BTC to ever be created:", max_money(), "Satoshis"
+

code/select-utxo.py

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+# Selects outputs from a UTXO list using a greedy algorithm.
+
+from sys import argv
+
+class OutputInfo:
+
+    def __init__(self, tx_hash, tx_index, value):
+        self.tx_hash = tx_hash
+        self.tx_index = tx_index
+        self.value = value
+
+    def __repr__(self):
+        return "<%s:%s with %s Satoshis>" % (self.tx_hash, self.tx_index,
+                                             self.value)
+
+# Select optimal outputs for a send from unspent outputs list.
+# Returns output list and remaining change to be sent to
+# a change address.
+def select_outputs_greedy(unspent, min_value):
+    # Fail if empty.
+    if not unspent:
+        return None
+    # Partition into 2 lists.
+    lessers = [utxo for utxo in unspent if utxo.value < min_value]
+    greaters = [utxo for utxo in unspent if utxo.value >= min_value]
+    key_func = lambda utxo: utxo.value
+    if greaters:
+        # Not-empty. Find the smallest greater.
+        min_greater = min(greaters)
+        change = min_greater.value - min_value
+        return [min_greater], change
+    # Not found in greaters. Try several lessers instead.
+    # Rearrange them from biggest to smallest. We want to use the least
+    # amount of inputs as possible.
+    lessers.sort(key=key_func, reverse=True)
+    result = []
+    accum = 0
+    for utxo in lessers:
+        result.append(utxo)
+        accum += utxo.value
+        if accum >= min_value:
+            change = accum - min_value
+            return result, "Change: %d Satoshis" % change
+    # No results found.
+    return None, 0
+
+def main():
+    unspent = [
+        OutputInfo("ebadfaa92f1fd29e2fe296eda702c48bd11ffd52313e986e99ddad9084062167", 1,  8000000),
+        OutputInfo("6596fd070679de96e405d52b51b8e1d644029108ec4cbfe451454486796a1ecf", 0,  16050000),
+        OutputInfo("b2affea89ff82557c60d635a2a3137b8f88f12ecec85082f7d0a1f82ee203ac4", 0,  10000000),
+        OutputInfo("7dbc497969c7475e45d952c4a872e213fb15d45e5cd3473c386a71a1b0c136a1", 0,  25000000),
+        OutputInfo("55ea01bd7e9afd3d3ab9790199e777d62a0709cf0725e80a7350fdb22d7b8ec6", 17,  5470541),
+        OutputInfo("12b6a7934c1df821945ee9ee3b3326d07ca7a65fd6416ea44ce8c3db0c078c64", 0,  10000000),
+        OutputInfo("7f42eda67921ee92eae5f79bd37c68c9cb859b899ce70dba68c48338857b7818", 0,  16100000),
+    ]
+    
+    if len(argv) > 1: 
+        target = long(argv[1])
+    else:
+        target = 55000000
+        
+    print "For transaction amount %d Satoshis (%f bitcoin) use: " % (target, target/10.0**8)
+    print select_outputs_greedy(unspent, target)
+
+if __name__ == "__main__":
+    main()
+