code: def test_uvars_calc_post_fit_method():
      """test using uvars and Model.post_fit method"""
  
      def post_fit(result):
          "example post fit function"
          result.params.add(
              "post_area", expr="g1_amplitude + g2_amplitude"
          )
  
      pars = nist_model.make_params(
          g1_center=110,
          g1_amplitude=4000,
          g1_sigma=25,
          g2_center=160,
          g2_amplitude=2000,
          g2_sigma=20,
          exp_amplitude=50,
          exp_decay=75,
      )
  
      _model = (
          ExponentialModel(prefix="exp_")
          + GaussianModel(prefix="g1_")
          + GaussianModel(prefix="g2_")
      )
  
      _model.post_fit = post_fit
      out = _model.fit(y, pars, x=x)
  
      assert out.nfev > 25
      assert out.errorbars
      assert out.chisqr > 1000
      assert out.chisqr < 3000
  
      post_area = out.params["post_area"]
  
      assert post_area.value > 6500
      assert post_area.value < 7000
  
      assert post_area.stderr > 43
      assert post_area.stderr < 48
  
file_path: lmfit-py/tests/test_params_uvars.py
imports: import os
  import numpy
  from lmfit import create_params, minimize
  from lmfit.models import ExponentialModel, GaussianModel
label_desc: Use image node_id 3 for calling a global function with example usage: test_uvars_calc_post_fit_method() without return types