Fall back to env vars to find height and width. Make the height-and-w…

…idth test run. Close erikrose#46.

README.rst

@@ -439,6 +439,8 @@ Version History
   * Make ``is_a_tty`` a read-only property, like ``does_styling``. Writing to
     it never would have done anything constructive.
   * Add ``fullscreen()`` and ``hidden_cursor()`` to the auto-generated docs.
+  * Fall back to ``LINES`` and ``COLUMNS`` environment vars to find height and
+    width. (jquast)
 
 1.5.1
   * Clean up fabfile, removing the redundant ``test`` command.

blessings/__init__.py

@@ -217,16 +217,28 @@ def width(self):
         return self._height_and_width()[1]
 
     def _height_and_width(self):
-        """Return a tuple of (terminal height, terminal width)."""
+        """Return a tuple of (terminal height, terminal width).
+
+        Start by trying TIOCGWINSZ (Terminal I/O-Control: Get Window Size),
+        falling back to environment variables (LINES, COLUMNS), and returning
+        (None, None) if those are unavailable or invalid.
+
+        """
         # tigetnum('lines') and tigetnum('cols') update only if we call
         # setupterm() again.
         for descriptor in self._init_descriptor, sys.__stdout__:
             try:
                 return struct.unpack(
                         'hhhh', ioctl(descriptor, TIOCGWINSZ, '\000' * 8))[0:2]
             except IOError:
+                # when the output stream or init descriptor is not a tty, such
+                # as when when stdout is piped to another program, fe. tee(1),
+                # these ioctls will raise IOError
                 pass
-        return None, None  # Should never get here
+        try:
+            return int(environ.get('LINES')), int(environ.get('COLUMNS'))
+        except TypeError:
+            return None, None
 
     @contextmanager
     def location(self, x=None, y=None):

blessings/tests.py

@@ -68,11 +68,11 @@ def test_parametrization():
     eq_(TestTerminal().cup(3, 4), unicode_parm('cup', 3, 4))
 
 
-def height_and_width():
+def test_height_and_width():
     """Assert that ``height_and_width()`` returns ints."""
     t = TestTerminal()  # kind shouldn't matter.
-    assert isinstance(int, t.height)
-    assert isinstance(int, t.width)
+    assert isinstance(t.height, int)
+    assert isinstance(t.width, int)
 
 
 def test_stream_attr():