Add test for probe timeout and fix for Python2

Fix for Python2 so that timeout is only used as keyword argument if it
is provided

Added a test for the new timeout argument that will run for Python >
3.3.

ffmpeg/_probe.py

@@ -18,7 +18,10 @@ def probe(filename, cmd='ffprobe', timeout=None, **kwargs):
     args += [filename]
 
     p = subprocess.Popen(args, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
-    out, err = p.communicate(timeout=timeout)
+    communicate_kwargs = {}
+    if timeout is not None:
+        communicate_kwargs['timeout'] = timeout
+    out, err = p.communicate(**communicate_kwargs)
     if p.returncode != 0:
         raise Error('ffprobe', out, err)
     return json.loads(out.decode('utf-8'))

ffmpeg/tests/test_ffmpeg.py

@@ -8,6 +8,7 @@ import pytest
 import random
 import re
 import subprocess
+import sys
 
 try:
     import mock  # python 2
@@ -706,6 +707,13 @@ def test__probe():
     assert data['format']['duration'] == '7.036000'
 
 
+@pytest.mark.skipif(sys.version_info < (3, 3), reason="requires python3.3 or higher")
+def test__probe_timeout():
+    with pytest.raises(subprocess.TimeoutExpired) as excinfo:
+        data = ffmpeg.probe(TEST_INPUT_FILE1, timeout=0)
+    assert 'timed out after 0 seconds' in str(excinfo.value)
+
+
 def test__probe__exception():
     with pytest.raises(ffmpeg.Error) as excinfo:
         ffmpeg.probe(BOGUS_INPUT_FILE)