cli should be able to write bytes to the output in python 3, too

test/test_wordcloud_cli.py

 import argparse
-import inspect
 from wordcloud import wordcloud_cli as cli
 import wordcloud as wc
 from collections import namedtuple
@@ -31,22 +30,12 @@ def all_arguments():
     return arguments
 
 
-def test_argument_spec_matches_to_constructor_args():
-    args = argparse.Namespace()
-    for option in all_arguments():
-        setattr(args, option.init_name, option.pass_value)
-
-    supported_args = inspect.getargspec(wc.WordCloud.__init__).args
-    supported_args.remove('self')
-    for arg_name in vars(args).keys():
-        assert_in(arg_name, supported_args)
-
-
 def test_main_passes_arguments_through():
     args = argparse.Namespace()
     for option in all_arguments():
         setattr(args, option.init_name, option.pass_value)
     args.imagefile = NamedTemporaryFile()
+    args.imagefile.buffer = MagicMock()
     args.text = 'some long text'
 
     with patch('wordcloud.wordcloud_cli.wc.WordCloud', autospec=True) as mock_word_cloud:

wordcloud/wordcloud_cli.py

@@ -10,7 +10,6 @@ import argparse
 import wordcloud as wc
 import numpy as np
 import sys
-import io
 from PIL import Image
 
 def main(args):
@@ -20,10 +19,9 @@ def main(args):
         color_func=args.color_func, background_color=args.background_color).generate(args.text)
     image = wordcloud.to_image()
 
-    b = io.BytesIO()
-    image.save(b, format='png')
     with args.imagefile:
-        args.imagefile.write(b.getvalue())
+        out = args.imagefile if sys.version < '3' else args.imagefile.buffer
+        image.save(out, format='png')
 
 def parse_args(arguments):
     prog = 'python wordcloud_cli.py'