code: def cat(pr_name, est_name, union="."):
      """Concat preprocess and estimator name if applicable."""
      if not pr_name:
          return est_name
      return union.join([pr_name, est_name])
  
file_path: mlens/mlens/model_selection/_base_functions.py
imports: from __future__ import division
  from collections import Counter
  from ..parallel import EvalLearner, EvalTransformer, Pipeline
  from ..utils.formatting import _assert_format
  from ..utils.checks import assert_valid_estimator
  from ..externals.sklearn.base import clone
label_desc: Use image node_id 3 for calling a global function with example usage: cat(pr_name, est_name, union) and returns: union, est_name