Solution for day 7.

day7.py

@@ -0,0 +1,65 @@
+import fileinput
+import re
+import sys
+
+recipe = {}
+values = {}
+
+def findValue(node):
+    match = re.search(r"\d+", node)
+    if match:
+        return int(match.group(0))
+
+    if node in values:
+        return values[node]
+
+    if node not in recipe:
+        sys.exit("Node without recipe '" + node + "'")
+
+    valueA = None
+    valueB = None
+    if recipe[node][0]:
+        valueA = findValue(recipe[node][0].strip())
+    if recipe[node][2]:
+        valueB = findValue(recipe[node][2])
+
+    action = recipe[node][1]
+    value = None
+    if action == "RSHIFT":
+        value = valueA >> valueB
+    elif action == "LSHIFT":
+        value = (valueA << valueB) & 0xffff
+    elif action == "NOT":
+        value = (~valueB) & 0xffff
+    elif action == "IS":
+        value = valueA & 0xffff
+    elif action == "AND":
+        value = valueA & valueB
+    elif action == "OR":
+        value = valueA | valueB
+    else:
+        sys.exit("Unsupported command " + action)
+
+    values[node] = value
+    return value
+
+opPattern = re.compile(r"(\w+ )?(RSHIFT|LSHIFT|NOT|AND|OR) (\w+) -> (\w+)")
+valuePattern = re.compile(r"(\w+) -> (\w+)")
+
+for line in fileinput.input():
+    match = valuePattern.match(line)
+    if match:
+        recipe[match.group(2)] = (match.group(1), "IS", "")
+    else:
+        match = opPattern.match(line)
+        if match.group(4) in recipe:
+            sys.exit("Node with multiple recipes")
+
+        recipe[match.group(4)] = (match.group(1), match.group(2), match.group(3))
+
+a = findValue("a")
+
+print "Initial a is ", a
+values = {}
+values["b"] = a
+print "Secondary a is", findValue("a")