Clean up Python 2 compatibility code.

python-package/xgboost/__init__.py

@@ -4,8 +4,6 @@
 Contributors: https://github.com/dmlc/xgboost/blob/master/CONTRIBUTORS.md
 """
 
-from __future__ import absolute_import
-
 import os
 
 from .core import DMatrix, Booster

python-package/xgboost/callback.py

@@ -1,7 +1,6 @@
 # coding: utf-8
 # pylint: disable=invalid-name, too-many-statements
 """Training Library containing training routines."""
-from __future__ import absolute_import
 
 from . import rabit
 from .core import EarlyStopException

python-package/xgboost/compat.py

@@ -1,30 +1,21 @@
 # coding: utf-8
 # pylint: disable= invalid-name,  unused-import
 """For compatibility and optional dependencies."""
-
-from __future__ import absolute_import
-
 import abc
 import os
 import sys
 
 from pathlib import PurePath
 
-PY3 = (sys.version_info[0] == 3)
+assert (sys.version_info[0] == 3), 'Python 2 is no longer supported.'
 
-if PY3:
-    # pylint: disable=invalid-name, redefined-builtin
-    STRING_TYPES = (str,)
+# pylint: disable=invalid-name, redefined-builtin
+STRING_TYPES = (str,)
 
-    def py_str(x):
-        """convert c string back to python string"""
-        return x.decode('utf-8')
-else:
-    STRING_TYPES = (basestring,)  # pylint: disable=undefined-variable
 
-    def py_str(x):
-        """convert c string back to python string"""
-        return x
+def py_str(x):
+    """convert c string back to python string"""
+    return x.decode('utf-8')
 
 
 ###############################################################################
@@ -87,12 +78,6 @@ def os_fspath(path):
 # END NUMPY PATHLIB ATTRIBUTION
 ###############################################################################
 
-# pickle
-try:
-    import cPickle as pickle  # noqa
-except ImportError:
-    import pickle  # noqa
-
 # pandas
 try:
     from pandas import DataFrame, Series

python-package/xgboost/core.py

@@ -18,7 +18,7 @@
 import scipy.sparse
 
 from .compat import (
-    STRING_TYPES, PY3, DataFrame, MultiIndex, py_str,
+    STRING_TYPES, DataFrame, MultiIndex, py_str,
     PANDAS_INSTALLED, DataTable,
     CUDF_INSTALLED, CUDF_DataFrame, CUDF_Series, CUDF_MultiIndex,
     os_fspath, os_PathLike)
@@ -70,11 +70,7 @@ def from_pystr_to_cstr(data):
     if not isinstance(data, list):
         raise NotImplementedError
     pointers = (ctypes.c_char_p * len(data))()
-    if PY3:
-        data = [bytes(d, 'utf-8') for d in data]
-    else:
-        data = [d.encode('utf-8') if isinstance(d, unicode) else d  # pylint: disable=undefined-variable
-                for d in data]
+    data = [bytes(d, 'utf-8') for d in data]
     pointers[:] = data
     return pointers
 
@@ -89,21 +85,12 @@ def from_cstr_to_pystr(data, length):
     length : ctypes pointer
         pointer to length of data
     """
-    if PY3:
-        res = []
-        for i in range(length.value):
-            try:
-                res.append(str(data[i].decode('ascii')))
-            except UnicodeDecodeError:
-                res.append(str(data[i].decode('utf-8')))
-    else:
-        res = []
-        for i in range(length.value):
-            try:
-                res.append(str(data[i].decode('ascii')))
-            except UnicodeDecodeError:
-                # pylint: disable=undefined-variable
-                res.append(unicode(data[i].decode('utf-8')))
+    res = []
+    for i in range(length.value):
+        try:
+            res.append(str(data[i].decode('ascii')))
+        except UnicodeDecodeError:
+            res.append(str(data[i].decode('utf-8')))
     return res
 
 

python-package/xgboost/rabit.py

@@ -1,14 +1,12 @@
 # coding: utf-8
 # pylint: disable= invalid-name
-
 """Distributed XGBoost Rabit related API."""
-from __future__ import absolute_import
 import sys
 import ctypes
+import pickle
 import numpy as np
 
 from .core import _LIB, c_str, STRING_TYPES
-from .compat import pickle
 
 
 def _init_rabit():

python-package/xgboost/tracker.py

@@ -5,8 +5,6 @@
 
 # pylint: disable=invalid-name, missing-docstring, too-many-arguments, too-many-locals
 # pylint: disable=too-many-branches, too-many-statements, too-many-instance-attributes
-from __future__ import absolute_import
-
 import socket
 import struct
 import time
@@ -336,4 +334,4 @@ def join(self):
             self.thread.join(100)
 
     def alive(self):
-        return self.thread.isAlive()
+        return self.thread.is_alive()

python-package/xgboost/training.py

@@ -2,8 +2,6 @@
 # pylint: disable=too-many-locals, too-many-arguments, invalid-name
 # pylint: disable=too-many-branches, too-many-statements
 """Training Library containing training routines."""
-from __future__ import absolute_import
-
 import numpy as np
 from .core import Booster, STRING_TYPES, XGBoostError, CallbackEnv, EarlyStopException
 from .compat import (SKLEARN_INSTALLED, XGBStratifiedKFold)

tests/python/regression_test_utilities.py

@@ -1,5 +1,3 @@
-from __future__ import print_function
-
 import glob
 import itertools as it
 import numpy as np

tests/python/test_linear.py

@@ -1,5 +1,3 @@
-from __future__ import print_function
-
 import numpy as np
 import testing as tm
 import unittest