def get_active_tape():
"""Returns the currently recording tape.
If no tape is currently recording, ``None`` is returned.
**Example**
>>> with qml.tape.QuantumTape():
... qml.RX(0.2, wires="a")
... tape = qml.tape.get_active_tape()
... qml.RY(0.1, wires="b")
>>> print(tape)
<QuantumTape: wires=['a', 'b'], params=2>
>>> print(qml.tape.get_active_tape())
None
"""
return QueuingContext.active_context()
def stop_recording(self):
"""Context manager to temporarily stop recording operations
onto the tape. This is useful is scratch space is needed.
**Example**
>>> with qml.tape.QuantumTape() as tape:
... qml.RX(0, wires=0)
... with tape.stop_recording():
... qml.RY(1.0, wires=1)
... qml.RZ(2, wires=1)
>>> tape.operations
[RX(0, wires=[0]), RZ(2, wires=[1])]
"""
if QueuingContext.active_context() is not self:
raise QueuingError("Cannot stop recording requested tape "
"as it is not currently recording.")
active_contexts = QueuingContext._active_contexts
QueuingContext._active_contexts = deque()
yield
QueuingContext._active_contexts = active_contexts