diff --git a/src/qiskit_qec/operators/pauli.py b/src/qiskit_qec/operators/pauli.py
index e0a01889..610583f5 100644
--- a/src/qiskit_qec/operators/pauli.py
+++ b/src/qiskit_qec/operators/pauli.py
@@ -99,7 +99,8 @@ def __init__(
                 )
 
         elif isinstance(data, str):
-            matrix, phase_exp = pauli_rep.str2symplectic(data, qubit_order=input_qubit_order)
+            matrix, phase_exp = pauli_rep.str2symplectic(
+                data, qubit_order=input_qubit_order)
         elif isinstance(data, ScalarOp):
             matrix, phase_exp = pauli_rep.scalar_op2symplectic(
                 data, output_encoding=pauli_rep.INTERNAL_PHASE_ENCODING
@@ -110,10 +111,12 @@ def __init__(
             if z is None:
                 # Using old Pauli initialization with positional args instead of kwargs
                 z = data
-            matrix, phase_exp = self._from_split_array_deprecated(z, x, phase_exp)
+            matrix, phase_exp = self._from_split_array_deprecated(
+                z, x, phase_exp)
 
         elif label is not None:  # DEPRECATED
-            matrix, phase_exp = self._from_label_deprecated(label, qubit_order=input_qubit_order)
+            matrix, phase_exp = self._from_label_deprecated(
+                label, qubit_order=input_qubit_order)
         else:
             raise QiskitError("Invalid input data for Pauli.")
 
@@ -197,11 +200,11 @@ def x(self, val):
     @property
     def z(self):
         """The z vector for the Pauli."""
-        return self.matrix[:, self.num_qubits :][0]
+        return self.matrix[:, self.num_qubits:][0]
 
     @z.setter
     def z(self, val):
-        self.matrix[:, self.num_qubits :][0] = val
+        self.matrix[:, self.num_qubits:][0] = val
 
     # ---------------------------------------------------------------------
     # Magic Methods
@@ -218,7 +221,7 @@ def __str__(self):
             and self.num_qubits > self._truncate__
             and BasePauli.EXTERNAL_SYNTAX == pauli_rep.PRODUCT_SYNTAX
         ):
-            front = self[-self._truncate__ :].to_label()
+            front = self[-self._truncate__:].to_label()
             return front + "..."
         return self.to_label()
 
@@ -319,7 +322,7 @@ def _getitem(self, i):
         Returns:
             Pauli: Pauli acting on qubit i
         """
-        return Pauli(self.matrix[0][i : self.matrix.shape[1] : self.num_qubits])
+        return Pauli(self.matrix[0][i: self.matrix.shape[1]: self.num_qubits])
 
     def _fast_getitem_str(self, i):
         """Get Pauli for qubit i
@@ -518,14 +521,15 @@ def to_instruction(self):
         )
 
         if len(pauli) == 1:
-            gate = {"I": IGate(), "X": XGate(), "Y": YGate(), "Z": ZGate()}[pauli]
+            gate = {"I": IGate(), "X": XGate(), "Y": YGate(),
+                    "Z": ZGate()}[pauli]
         else:
             gate = PauliGate(pauli)
-        if not phase_exp[0]:
+        if not phase_exp:
             return gate
         # Add global phase
         circuit = QuantumCircuit(self.num_qubits, name=str(self))
-        circuit.global_phase = -phase_exp[0] * pi / 2
+        circuit.global_phase = -phase_exp * pi / 2
         circuit.append(gate, range(self.num_qubits))
         return circuit.to_instruction()
 
@@ -696,7 +700,8 @@ def instrs2symplectic(instr: Union[Instruction, QuantumCircuit]):
             instr = instr.definition
 
         # Initialize identity Pauli
-        ret = Pauli(np.zeros((1, 2 * instr.num_qubits), dtype=bool), phase_exp=0)
+        ret = Pauli(np.zeros((1, 2 * instr.num_qubits),
+                    dtype=bool), phase_exp=0)
         # Add circuit global phase if specified
         if instr.global_phase:
             ret._phase_exp = pauli_rep.cpx2exp(
@@ -948,7 +953,8 @@ def insert_paulis(self, indices=None, paulis=None, pauli_labels=None):
         """
         if pauli_labels is not None:
             if paulis is not None:
-                raise QiskitError("Please only provide either `paulis` or `pauli_labels`")
+                raise QiskitError(
+                    "Please only provide either `paulis` or `pauli_labels`")
             if isinstance(pauli_labels, str):
                 pauli_labels = list(pauli_labels)
             # since pauli label is in reversed order.
@@ -1032,7 +1038,8 @@ def pauli_single(cls, num_qubits, index, pauli_label):
             Pauli: single qubit pauli
         """
         tmp = Pauli(pauli_label)
-        ret = Pauli((np.zeros(num_qubits, dtype=bool), np.zeros(num_qubits, dtype=bool)))
+        ret = Pauli((np.zeros(num_qubits, dtype=bool),
+                    np.zeros(num_qubits, dtype=bool)))
         ret.x[index] = tmp.x[0]
         ret.z[index] = tmp.z[0]
         ret.phase = tmp.phase
@@ -1057,7 +1064,8 @@ def random(cls, num_qubits, seed=None):
             Pauli: the random pauli
         """
         # pylint: disable=cyclic-import
-        from qiskit.quantum_info.operators.symplectic.random import random_pauli
+        from qiskit.quantum_info.operators.symplectic.random import \
+            random_pauli
 
         return random_pauli(num_qubits, group_phase=False, seed=seed)