diff --git a/2015/day7-defer.py b/2015/day7-defer.py
new file mode 100644
index 0000000..b0cf290
--- /dev/null
+++ b/2015/day7-defer.py
@@ -0,0 +1,69 @@
+with open('day7-input', 'r') as file:
+  data = [l.strip('\n') for l in file]
+TOKENS = [line.split(' ') for line in data]
+bin_ops = {'AND': int.__and__, 'OR': int.__or__, 'RSHIFT': int.__rshift__, 'LSHIFT': int.__lshift__}
+
+class dict_int_giver(dict):
+  def __init__(self, kvs=[], readonly=None):
+    super().__init__(kvs)
+    self.readonly = set()
+    if readonly:
+      self.readonly = set(readonly)
+  def __getitem__(self, key):
+    try:
+      return int(key.replace(',', ''))
+    except ValueError:
+      return dict.get(self, key, None)
+  def __setitem__(self, key, value):
+    if key in self.readonly:
+      return
+    dict.__setitem__(self, key, value)
+
+def run_circuit(identifiers):
+  stack = [line for line in reversed(TOKENS)]
+
+  deferred = {}
+  def defer(until_identifier, tokens):
+    if until_identifier in deferred:
+      deferred[until_identifier].append(tokens)
+    else:
+      deferred[until_identifier] = [tokens]
+
+  while stack:
+    tokens = stack.pop()
+    output = tokens[-1]
+    input = tokens[:-2]
+    if len(input) == 1:  # Can only be a -> b
+      i = identifiers[input[0]]
+      if i is not None:
+        identifiers[output] = i
+        if output in deferred:
+          stack += deferred.pop(output)
+      else:
+        defer(input[0], tokens)
+    elif len(input) == 2:  # Can only be NOT a -> b. a must be identifier.
+      if input[1] in identifiers:
+        identifiers[output] = identifiers[input[1]] ^ 0xFFFF  # 16bit values
+        if output in deferred:
+          stack += deferred.pop(output)
+      else:
+        defer(input[1], tokens)
+    elif len(input) == 3:  # Can be any of the binary operators
+      i = identifiers[input[0]]
+      j = identifiers[input[2]]
+      if i is None:
+        defer(input[0], tokens)
+        continue
+      if j is None:
+        defer(input[2], tokens)
+        continue
+      identifiers[output] = bin_ops[input[1]](i, j) & 0xFFFF
+      if output in deferred:
+        stack += deferred.pop(output)
+
+identifiers_1 = dict_int_giver()
+run_circuit(identifiers_1)
+print(identifiers_1['a'])  # Part 1
+identifiers_2 = dict_int_giver([ ['b', identifiers_1['a'] ] ], ['b'])
+run_circuit(identifiers_2)
+print(identifiers_2['a'])  # Part 2