BUG allow to import keras from tensorflow (#532)

Author: glemaitre

doc/whats_new/v0.5.rst

@@ -77,3 +77,7 @@ Bug
   :class:`imblearn.ensemble.RUSBoostClassifier` to get a decision stump as a
   weak learner as in the original paper.
   :pr:`545` by :user:`Christos Aridas <chkoar>`.
+
+- Allow to import ``keras`` directly from ``tensorflow`` in the
+  :mod:`imblearn.keras`.
+  :pr:`531` by :user:`Guillaume Lemaitre <glemaitre>`.

imblearn/keras/_generator.py

@@ -1,16 +1,43 @@
 """Implement generators for ``keras`` which will balance the data."""
-from __future__ import division
+
 
 # This is a trick to avoid an error during tests collection with pytest. We
 # avoid the error when importing the package raise the error at the moment of
 # creating the instance.
-try:
-    import keras
-    ParentClass = keras.utils.Sequence
-    HAS_KERAS = True
-except ImportError:
-    ParentClass = object
-    HAS_KERAS = False
+def import_keras():
+    """Try to import keras from keras and tensorflow.
+
+    This is possible to import the sequence from keras or tensorflow.
+    Keras is not ducktyping ``Sequence`` before 2.3 and we need import from
+    all possible library to ensure that the ``isinstance(...)`` is not going
+    to fail. This function can be modified when we support Keras 2.3.
+    """
+
+    def import_from_keras():
+        try:
+            import keras
+            return (keras.utils.Sequence,), True
+        except ImportError:
+            return tuple(), False
+
+    def import_from_tensforflow():
+        try:
+            from tensorflow import keras
+            return (keras.utils.Sequence,), True
+        except ImportError:
+            return tuple(), False
+
+    ParentClassKeras, has_keras_k = import_from_keras()
+    ParentClassTensorflow, has_keras_tf = import_from_tensforflow()
+    has_keras = has_keras_k or has_keras_tf
+    if has_keras:
+        ParentClass = (ParentClassKeras + ParentClassTensorflow)
+    else:
+        ParentClass = (object,)
+    return ParentClass, has_keras
+
+
+ParentClass, HAS_KERAS = import_keras()
 
 from scipy.sparse import issparse
 
@@ -29,7 +56,7 @@
                           'NeighbourhoodCleaningRule', 'TomekLinks')
 
 
-class BalancedBatchGenerator(ParentClass):
+class BalancedBatchGenerator(*ParentClass):
     """Create balanced batches when training a keras model.
 
     Create a keras ``Sequence`` which is given to ``fit_generator``. The
@@ -102,6 +129,10 @@ class BalancedBatchGenerator(ParentClass):
     ...                                        epochs=10, verbose=0)
 
     """
+
+    # flag for keras sequence duck-typing
+    use_sequence_api = True
+
     def __init__(self, X, y, sample_weight=None, sampler=None, batch_size=32,
                  keep_sparse=False, random_state=None):
         if not HAS_KERAS: