code: def pauli_word_prefactor(observable):
      """If the operator provided is a valid Pauli word (i.e a single term which may be a tensor product
      of pauli operators), then this function extracts the prefactor.
  
      Args:
          observable (~.Operator): the operator to be examined
  
      Returns:
          Union[int, float, complex]: The scaling/phase coefficient of the Pauli word.
  
      Raises:
          ValueError: If an operator is provided that is not a valid Pauli word.
  
      **Example**
  
      >>> pauli_word_prefactor(qml.Identity(0))
      1
      >>> pauli_word_prefactor(qml.PauliX(0) @ qml.PauliY(1))
      1
      >>> pauli_word_prefactor(qml.PauliX(0) @ qml.PauliY(0))
      1j
      """
      return _pauli_word_prefactor(observable)
  
file_path: pennylane/pennylane/pauli/pauli_interface.py
imports: from typing import Union
  from functools import singledispatch
  from pennylane.ops import Hamiltonian, Identity, PauliX, PauliY, PauliZ, Prod, SProd
  from pennylane.operation import Tensor
  from .utils import is_pauli_word
  from .conversion import pauli_sentence
label_desc: Use image node_id 1 for calling a global function with example usage: pauli_word_prefactor(observable) and returns: _pauli_word_prefactor