Printer: Allow closing

Now every printer can be closed, only ClosablePrinter's *need* to be
closed.

coalib/output/printers/ClosablePrinter.py

@@ -7,19 +7,6 @@ class ClosablePrinter(Printer):
     programmer will be warned, hopefully the user will never see any
     functionality coming from this printer.
     """
-    def __init__(self):
-        Printer.__init__(self)
-
-        self._closed = False
-
-    def _close(self):
-        pass
-
-    def close(self):
-        if not self._closed:
-            self._close()
-            self._closed = True
-
     def __del__(self):  # pragma: no cover
         """
         May warn if not closed properly - programmer error!

coalib/output/printers/Printer.py

@@ -12,6 +12,16 @@ class Printer:
     - EspeakPrinter for Voice output
     - NullPrinter for no output
     """
+    def __init__(self):
+        self._closed = False
+
+    def _close(self):
+        pass
+
+    def close(self):
+        if not self._closed:
+            self._close()
+            self._closed = True
 
     def _print(self, output, **kwargs):
         """
@@ -37,6 +47,7 @@ def print(self, *args, delimiter=' ', end='\n', **kwargs):
         :param kwargs:    Will be passed through to the Printer derivative
                           handling the actual printing
         """
+        assert not self._closed, "Cannot print after closing."
         output = str(delimiter).join(str(arg) for arg in args) + str(end)
 
         return self._print(output, **kwargs)

coalib/tests/output/printers/PrinterTest.py

@@ -15,6 +15,11 @@ def test_printer_interface(self):
         self.uut = Printer()
         self.assertRaises(NotImplementedError, self.uut.print, "test")
 
+    def test_closed_printing(self):
+        self.uut = TestPrinter()
+        self.uut.close()
+        self.assertRaises(AssertionError, self.uut.print)
+
     def test_printer_concatenation(self):
         self.uut = TestPrinter()
         self.assertEqual(self.uut.print("hello",