title: Sklearn validation_curve : Which possibilities do I have for the "param_name" parameter
body: <p>If I calculate the <a href="http://scikit-learn.org/stable/modules/generated/sklearn.model_selection.validation_curve.html#sklearn.model_selection.validation_curve" rel="nofollow noreferrer">validation curve</a> like follows:</p>
  
  <pre><code>PolynomialRegression(degree=2,**kwargs):
      return make_pipeline(PolynomialFeatures(degree),LinearRegression(**kwargs))
  
  #...
  
  degree=np.arange(0,21)
  
  train_score,val_score=validation_curve(PolynomialRegression(),X,y,"polynomialfeatures__degree",degree,cv=7)
  </code></pre>
  
  <p>the function claims the parameter "param_name" which is the name of the parameter that will be evaluated ("param_range") In this case it is polynomialfeatures__degree.
  But:</p>
  
  <ol>
  <li>From where do I get the string for "param_name" in general and from where do I get the string "polynomialfeatures__degree" in particular because I can't find this param_name in any documentation...Is the "function__param name" a common way to point on the param_name of a function??</li>
  <li>For which estimators can I use the validation_curve function? </li>
  </ol>