Remove python2 support and update python/spark versions (#206)

remove python2 testing in travis CI
test with python3.7 instead of python3.6
update spark version to 2.4.4. instead of 2.4.3

Author: Loquats

.travis.yml

@@ -7,12 +7,11 @@ language: minimal
 env:
   global:
     - DOCKER_COMPOSE_VERSION=1.22.0
+    - PYTHON_VERSION=3.7
   matrix:
-    - PYTHON_VERSION=3.6 TEST_SUITE=pylint
-    - PYTHON_VERSION=2.7 TEST_SUITE=pylint
-    - PYTHON_VERSION=3.6 TEST_SUITE=python-tests
-    - PYTHON_VERSION=2.7 TEST_SUITE=python-tests
-    - PYTHON_VERSION=3.6 TEST_SUITE=scala-tests
+    - TEST_SUITE=pylint
+    - TEST_SUITE=python-tests
+    - TEST_SUITE=scala-tests
 
 services:
   - docker

Dockerfile

@@ -40,7 +40,7 @@ RUN /opt/conda/bin/conda create -n sparkdl python=$PYTHON_VERSION && \
 
 # Install Spark and update env variables.
 ENV SCALA_VERSION 2.11.8
-ENV SPARK_VERSION 2.4.3
+ENV SPARK_VERSION 2.4.4
 ENV SPARK_BUILD "spark-${SPARK_VERSION}-bin-hadoop2.7"
 ENV SPARK_BUILD_URL "https://dist.apache.org/repos/dist/release/spark/spark-${SPARK_VERSION}/${SPARK_BUILD}.tgz"
 RUN wget --quiet $SPARK_BUILD_URL -O /tmp/spark.tgz && \

build.sbt

@@ -3,7 +3,7 @@
 
 import ReleaseTransformations._
 
-val sparkVer = sys.props.getOrElse("spark.version", "2.4.3")
+val sparkVer = sys.props.getOrElse("spark.version", "2.4.4")
 val sparkBranch = sparkVer.substring(0, 3)
 val defaultScalaVer = sparkBranch match {
   case "2.3" => "2.11.8"

dev/run.py

@@ -122,7 +122,7 @@ def print_if(cond, *args):
 
 def _get_required_env(default=False, interactive=False, override=False, verbose=False):
     default_env = {'PYSPARK_PYTHON': 'python',
-                   'SPARK_VERSION': '2.3.1',
+                   'SPARK_VERSION': '2.4.4',
                    'SPARK_HOME': os.path.join(HOME, 'bin/spark-2.3.1-bin-hadoop2.7/'),
                    'SCALA_VERSION': '2.11.8'}
 

python/sparkdl/estimators/keras_image_file_estimator.py

@@ -69,10 +69,6 @@ def __next__(self):
             self.counter += 1
         return self.models[index]
 
-    def next(self):
-        """For python2 compatibility."""
-        return self.__next__()
-
 
 class KerasImageFileEstimator(Estimator, HasInputCol, HasOutputCol, HasLabelCol, HasKerasModel,
                               HasKerasOptimizer, HasKerasLoss, CanLoadImage, HasOutputMode):