qiskit/extensions/simulator/snapshot.py
def snapshot(self,
             label,
             snapshot_type='statevector',
             qubits=None,
             params=None):
    """Take a statevector snapshot of the internal simulator representation.
    Works on all qubits, and prevents reordering (like barrier).

    For other types of snapshots use the Snapshot extension directly.

    Args:
        label (str): a snapshot label to report the result
        snapshot_type (str): the type of the snapshot.
        qubits (list or None): the qubits to apply snapshot to [Default: None].
        params (list or None): the parameters for snapshot_type [Default: None].

    Returns:
        QuantumCircuit: with attached command

    Raises:
        ExtensionError: malformed command
    """
    # Convert label to string for backwards compatibility
    if not isinstance(label, str):
        warnings.warn(
            "Snapshot label should be a string, "
            "implicit conversion is depreciated.", DeprecationWarning)
        label = str(label)
    # If no qubits are specified we add all qubits so it acts as a barrier
    # This is needed for full register snapshots like statevector
    if isinstance(qubits, QuantumRegister):
        qubits = qubits[:]
    if not qubits:
        tuples = []
        if isinstance(self, QuantumCircuit):
            for register in self.qregs:
                tuples.append(register)
        if not tuples:
            raise ExtensionError('no qubits for snapshot')
        qubits = []
        for tuple_element in tuples:
            if isinstance(tuple_element, QuantumRegister):
                for j in range(tuple_element.size):
                    qubits.append((tuple_element, j))
            else:
                qubits.append(tuple_element)
    return self.append(
        Snapshot(
            label,
            snapshot_type=snapshot_type,
            num_qubits=len(qubits),
            params=params), qubits)
def snapshot(self,
             label,
             snapshot_type='statevector',
             qubits=None,
             params=None):
    """Take a statevector snapshot of the internal simulator representation.
    Works on all qubits, and prevents reordering (like barrier).

    For other types of snapshots use the Snapshot extension directly.

    Args:
        label (str): a snapshot label to report the result
        snapshot_type (str): the type of the snapshot.
        qubits (list or None): the qubits to apply snapshot to [Default: None].
        params (list or None): the parameters for snapshot_type [Default: None].

    Returns:
        QuantumCircuit: with attached command

    Raises:
        ExtensionError: malformed command
    """
    # Convert label to string for backwards compatibility
    if not isinstance(label, str):
        warnings.warn(
            "Snapshot label should be a string, "
            "implicit conversion is depreciated.", DeprecationWarning)
        label = str(label)
    # If no qubits are specified we add all qubits so it acts as a barrier
    # This is needed for full register snapshots like statevector
    if isinstance(qubits, QuantumRegister):
        qubits = qubits[:]
    if not qubits:
        tuples = []
        if isinstance(self, QuantumCircuit):
            for register in self.qregs:
                tuples.append(register)
        if not tuples:
            raise ExtensionError('no qubits for snapshot')
        qubits = []
        for tuple_element in tuples:
            if isinstance(tuple_element, QuantumRegister):
                for j in range(tuple_element.size):
                    qubits.append((tuple_element, j))
            else:
                qubits.append(tuple_element)
    return self.append(
        Snapshot(
            label,
            snapshot_type=snapshot_type,
            num_qubits=len(qubits),
            params=params), qubits)
Take a statevector snapshot of the internal simulator representation.
    Works on all qubits, and prevents reordering (like barrier).

    For other types of snapshots use the Snapshot extension directly.

    Args:
        label (str): a snapshot label to report the result
        snapshot_type (str): the type of the snapshot.
        qubits (list or None): the qubits to apply snapshot to [Default: None].
        params (list or None): the parameters for snapshot_type [Default: None].

    Returns:
        QuantumCircuit: with attached command

    Raises:
        ExtensionError: malformed command