added deprecation warning (#238)

* added deprecation warning
Co-authored-by: ragrawal <[email protected]>

Author: ragrawal

sklearn_pandas/transformers.py

@@ -1,6 +1,7 @@
 import numpy as np
 import pandas as pd
 from sklearn.base import TransformerMixin
+import warnings
 
 
 def _get_mask(X, value):
@@ -30,6 +31,11 @@ def __init__(self, func):
                 in SUPPORTED_FUNCTIONS variable. Throws assertion error if the
                 not supported.
         """
+
+        warnings.warn("""
+            NumericalTransformer is deprecated. Please write your own
+            transformer using Sklearn.base.TransformerMixin class
+            """, DeprecationWarning)
         assert func in self.SUPPORTED_FUNCTIONS, \
             f"Only following func are supported: {self.SUPPORTED_FUNCTIONS}"
         super(NumericalTransformer, self).__init__()