diff --git a/python-package/xgboost/callback.py b/python-package/xgboost/callback.py
index 16e0acf74a1c..2c6d3a704817 100644
--- a/python-package/xgboost/callback.py
+++ b/python-package/xgboost/callback.py
@@ -51,7 +51,7 @@ def callback(env):
         if env.rank != 0 or (not env.evaluation_result_list) or period is False or period == 0:
             return
         i = env.iteration
-        if (i % period == 0 or i + 1 == env.begin_iteration or i + 1 == env.end_iteration):
+        if i % period == 0 or i + 1 == env.begin_iteration or i + 1 == env.end_iteration:
             msg = '\t'.join([_fmt_metric(x, show_stdv) for x in env.evaluation_result_list])
             rabit.tracker_print('[%d]\t%s\n' % (i, msg))
     return callback
diff --git a/python-package/xgboost/core.py b/python-package/xgboost/core.py
index 644dcf8f7348..ff147403707f 100644
--- a/python-package/xgboost/core.py
+++ b/python-package/xgboost/core.py
@@ -241,7 +241,7 @@ def _maybe_pandas_data(data, feature_names, feature_types):
     if feature_names is None:
         if isinstance(data.columns, MultiIndex):
             feature_names = [
-                ' '.join(map(str, i))
+                ' '.join([str(x) for x in i])
                 for i in data.columns
             ]
         else:
@@ -1716,7 +1716,7 @@ def get_split_value_histogram(self, feature, fmap='', bins=None, as_pandas=True)
         regexp = re.compile(r"\[{0}<([\d.Ee+-]+)\]".format(feature))
         for i, _ in enumerate(xgdump):
             m = re.findall(regexp, xgdump[i])
-            values.extend(map(float, m))
+            values.extend([float(x) for x in m])
 
         n_unique = len(np.unique(values))
         bins = max(min(n_unique, bins) if bins is not None else n_unique, 1)
diff --git a/python-package/xgboost/training.py b/python-package/xgboost/training.py
index 111fbc019ba2..71c96736a80e 100644
--- a/python-package/xgboost/training.py
+++ b/python-package/xgboost/training.py
@@ -49,7 +49,7 @@ def _train_internal(params, dtrain,
 
     # Distributed code: Load the checkpoint from rabit.
     version = bst.load_rabit_checkpoint()
-    assert(rabit.get_world_size() != 1 or version == 0)
+    assert rabit.get_world_size() != 1 or version == 0
     rank = rabit.get_rank()
     start_iteration = int(version / 2)
     nboost += start_iteration
@@ -75,7 +75,7 @@ def _train_internal(params, dtrain,
             bst.save_rabit_checkpoint()
             version += 1
 
-        assert(rabit.get_world_size() == 1 or version == rabit.version_number())
+        assert rabit.get_world_size() == 1 or version == rabit.version_number()
 
         nboost += 1
         evaluation_result_list = []
diff --git a/tests/travis/setup.sh b/tests/travis/setup.sh
index f137de76fdfe..7618b84f5997 100755
--- a/tests/travis/setup.sh
+++ b/tests/travis/setup.sh
@@ -1,7 +1,7 @@
 #!/bin/bash
 
 if [ ${TASK} == "lint" ]; then
-    pip3 install --user cpplint 'pylint==1.4.4' 'astroid==1.3.6'
+    pip3 install --user cpplint 'pylint==1.4.4' 'astroid==1.3.6' numpy scipy
 fi