Support Qureg.__int__ for multiple bits (little-endian)

projectq/types/_qubit.py

@@ -181,17 +181,12 @@ def __bool__(self):
 
  def __int__(self):
  """
- Return measured value if Qureg consists of 1 qubit only.
+ Return the measured little-endian integer in the quregister.
 
  Raises:
- Exception if more than 1 qubit resides in this register (then you
- need to specify which value to get using qureg[???])
+ NotYetMeasuredError if any of the qubits isn't measured.
  """
- if len(self) == 1:
- return int(self[0])
- else:
- raise Exception("__int__(qureg): Quantum register contains more "
- "than 1 qubit. Use __bool__(qureg[idx]) instead.")
+ return sum(1 << i if bool(self[i]) else 0 for i in range(len(self)))
 
  def __nonzero__(self):
  """

projectq/types/_qubit_test.py

@@ -154,6 +154,34 @@ def test_qureg_measure_if_qubit():
  assert qureg1.__nonzero__()
 
 
+def test_qureg_measure_multi_qubit_int():
+ eng = MainEngine(backend=DummyEngine(), engine_list=[DummyEngine()])
+ a = eng.allocate_qureg(4)
+
+ assert int(_qubit.Qureg([])) == 0
+
+ eng.set_measurement_result(a[3], False)
+ eng.set_measurement_result(a[2], True)
+ eng.set_measurement_result(a[1], False)
+ eng.set_measurement_result(a[0], True)
+ assert int(a) == 0b0101
+ assert int(_qubit.Qureg(reversed(a))) == 0b1010
+ assert int(_qubit.Qureg([a[0], a[2], a[1], a[3]])) == 0b0011
+ assert int(_qubit.Qureg([a[0], a[1]])) == 0b01
+
+ eng.set_measurement_result(a[3], True)
+ eng.set_measurement_result(a[2], True)
+ eng.set_measurement_result(a[1], True)
+ eng.set_measurement_result(a[0], True)
+ assert int(a) == 15
+
+ eng.set_measurement_result(a[3], False)
+ eng.set_measurement_result(a[2], False)
+ eng.set_measurement_result(a[1], False)
+ eng.set_measurement_result(a[0], True)
+ assert int(a) == 1
+
+
 def test_qureg_measure_exception():
  eng = MainEngine(backend=DummyEngine(), engine_list=[DummyEngine()])
  qureg = _qubit.Qureg()