code: def get_imputer(imputer_name):
      if imputer_name is None:
          return None
      if imputer_name == "median":
          return impute.SimpleImputer(strategy="median")
      if imputer_name == "mean":
          return impute.SimpleImputer(strategy="mean")
      if imputer_name == "most_frequent":
          return impute.SimpleImputer(strategy="most_frequent")
      raise ValueError("Invalid imputer")
  
imports: import copy
  from collections import defaultdict
  from dataclasses import dataclass
  from functools import partial
  from typing import List, Optional
  import numpy
  from sklearn import ensemble, impute, linear_model
  from sklearn import metrics
  from sklearn import naive_bayes, neighbors, pipeline, preprocessing, svm, tree
  from xgboost import XGBClassifier, XGBRegressor
label_desc: Use image node_id 2 for calling a global function with example usage: get_imputer(imputer_name) and returns: None, impute, impute, impute