Use importlib to import user calibration module

Signed-off-by: Jim Easterbrook <jim@jim-easterbrook.me.uk>

src/pywws/__init__.py

@@ -1,3 +1,3 @@
 __version__ = '18.5.0'
-_release = '1531'
-_commit = '0ed083c'
+_release = '1532'
+_commit = 'ac9c014'

src/pywws/calib.py

@@ -1,6 +1,6 @@
 # pywws - Python software for USB Wireless Weather Stations
 # http://github.com/jim-easterbrook/pywws
-# Copyright (C) 2008-14  Jim Easterbrook  jim@jim-easterbrook.me.uk
+# Copyright (C) 2008-18  pywws contributors
 
 # This program is free software; you can redistribute it and/or
 # modify it under the terms of the GNU General Public License
@@ -83,12 +83,14 @@ def calib(self, raw):
 
 __docformat__ = "restructuredtext en"
 
+import importlib
 import logging
 import os
 import sys
 
 logger = logging.getLogger(__name__)
 
+
 class DefaultCalib(object):
     """Default calibration class.
 
@@ -106,8 +108,10 @@ def calib(self, raw):
         result['rel_pressure'] = result['abs_pressure'] + self.pressure_offset
         return result
 
+
 usercalib = None
 
+
 class Calib(object):
     """Calibration class that implements default or user calibration.
 
@@ -129,8 +133,8 @@ def __init__(self, params, stored_data):
                 path, module = os.path.split(user_module)
                 sys.path.insert(0, path)
                 module = os.path.splitext(module)[0]
-                usercalib = __import__(
-                    module, globals(), locals(), ['Calib'])
+                usercalib = importlib.import_module(module)
+                del sys.path[0]
                 Calib.calibrator = usercalib.Calib(params, stored_data)
             else:
                 logger.info('Using default calibration')