class_docstr: pass a custom callback function
  
  This makes sure it's being used.
class_docstr_tok: ["pass","a","custom","callback","function","This","makes","sure","it","'s","being","used","."]
code: def __call__(self, x):
      self.been_called = True
      self.ncalls += 1
  
imports: from numpy.testing import assert_, assert_array_almost_equal, assert_allclose, assert_equal
  from pytest import raises
  import pytest
  import numpy
  from scipy.optimize import fmin_slsqp, minimize, Bounds, NonlinearConstraint
label_desc: Use image node_id 2 for calling the MyCallBack obj's underlying member method code with example usage: obj.__call__(x) without return types