Changed how the pipe file descriptors get opened on Python 3 vs 2

Open them in text mode in Python 3 so self.stdout.write() expects normal Python 3 (unicode) strings.

Open them in binary mode in Python 2 so self.stdout.write() expects normal Python 2 (byte) strings.

Also fixed a unit test mocking issue on Python 2 to account for the fact that Python 2.7 requires the subprocess32 module instead of subprocess.

Author: tleonhardt

cmd2.py

@@ -776,11 +776,18 @@ def _redirect_output(self, statement):
             # Create a pipe with read and write sides
             read_fd, write_fd = os.pipe()
 
+            # Make sure that self.stdout.write() expects unicode strings in Python 3 and byte strings in Python 2
+            write_mode = 'w'
+            read_mode = 'r'
+            if six.PY2:
+                write_mode = 'wb'
+                read_mode = 'rb'
+
             # Open each side of the pipe and set stdout accordingly
             # noinspection PyTypeChecker
-            self.stdout = io.open(write_fd, 'w')
+            self.stdout = io.open(write_fd, write_mode)
             # noinspection PyTypeChecker
-            subproc_stdin = io.open(read_fd, 'r')
+            subproc_stdin = io.open(read_fd, read_mode)
 
             # If you don't set shell=True, subprocess failure will throw an exception
             try:

tests/test_cmd2.py

@@ -113,7 +113,10 @@ def test_set_quiet(base_app):
 
 def test_base_shell(base_app, monkeypatch):
     m = mock.Mock()
-    monkeypatch.setattr("subprocess.Popen", m)
+    subprocess = 'subprocess'
+    if six.PY2:
+        subprocess = 'subprocess32'
+    monkeypatch.setattr("{}.Popen".format(subprocess), m)
     out = run_cmd(base_app, 'shell echo a')
     assert out == []
     assert m.called
@@ -554,7 +557,6 @@ def test_pipe_to_shell(base_app, capsys):
         # Windows
         command = 'help | sort'
         # Get help menu and pipe it's output to the sort shell command
-        run_cmd(base_app, 'help | sort')
         # expected = ['', '', '_relative_load  edit  history  py        quit  save  shell      show',
         #             '========================================',
         #             'cmdenvironment  help  load     pyscript  run   set   shortcuts',
@@ -578,15 +580,17 @@ def test_pipe_to_shell(base_app, capsys):
     # access to the output produced by that subprocess within a unit test, but we can verify that no error occured
     assert not err
 
-
-
 def test_pipe_to_shell_error(base_app, capsys):
     # Try to pipe command output to a shell command that doesn't exist in order to produce an error
     run_cmd(base_app, 'help | foobarbaz.this_does_not_exist')
     out, err = capsys.readouterr()
 
     assert not out
-    assert err.startswith("EXCEPTION of type 'FileNotFoundError' occurred with message:")
+
+    expected_error = 'FileNotFoundError'
+    if six.PY2:
+        expected_error = 'OSError'
+    assert err.startswith("EXCEPTION of type '{}' occurred with message:".format(expected_error))
 
 
 @pytest.mark.skipif(not cmd2.can_clip,