code: def apply_grover(oracle, nqubits, iterations=None):
      """Applies grover's algorithm.
  
      Parameters
      ==========
  
      oracle : callable
          The unknown callable function that returns true when applied to the
          desired qubits and false otherwise.
  
      Returns
      =======
  
      state : Expr
          The resulting state after Grover's algorithm has been iterated.
  
      Examples
      ========
  
      Apply grover's algorithm to an even superposition of 2 qubits::
  
          >>> from sympy.physics.quantum.qapply import qapply
          >>> from sympy.physics.quantum.qubit import IntQubit
          >>> from sympy.physics.quantum.grover import apply_grover
          >>> f = lambda qubits: qubits == IntQubit(2)
          >>> qapply(apply_grover(f, 2))
          |2>
  
      """
      if nqubits <= 0:
          raise QuantumError(
              "Grover's algorithm needs nqubits > 0, received %r qubits"
              % nqubits
          )
      if iterations is None:
          iterations = floor(sqrt(2**nqubits) * (pi / 4))
  
      v = OracleGate(nqubits, oracle)
      iterated = superposition_basis(nqubits)
      for iter in range(iterations):
          iterated = grover_iteration(iterated, v)
          iterated = qapply(iterated)
  
      return iterated
  
imports: from sympy.core.numbers import pi
  from sympy.core.sympify import sympify
  from sympy.core.basic import Atom
  from sympy.functions.elementary.integers import floor
  from sympy.functions.elementary.miscellaneous import sqrt
  from sympy.matrices.dense import eye
  from sympy.core.numbers import NegativeOne
  from sympy.physics.quantum.qapply import qapply
  from sympy.physics.quantum.qexpr import QuantumError
  from sympy.physics.quantum.hilbert import ComplexSpace
  from sympy.physics.quantum.operator import UnitaryOperator
  from sympy.physics.quantum.gate import Gate
  from sympy.physics.quantum.qubit import IntQubit
label_desc: Use image node_id 3 for calling a global function with example usage: apply_grover(oracle, nqubits, iterations) and returns: iterated