Issue #13609: Add two functions to query the terminal size:

os.get_terminal_size (low level) and shutil.get_terminal_size (high level).
Patch by Zbigniew Jędrzejewski-Szmek.

Doc/library/os.rst

@@ -1411,6 +1411,43 @@ or `the MSDN <http://msdn.microsoft.com/en-us/library/z0kc8e3z.aspx>`_ on Window
    .. versionadded:: 3.3
 
 
+.. _terminal-size:
+
+Querying the size of a terminal
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. versionadded:: 3.3
+
+.. function:: get_terminal_size(fd=STDOUT_FILENO)
+
+   Return the size of the terminal window as ``(columns, lines)``,
+   tuple of type :class:`terminal_size`.
+
+   The optional argument ``fd`` (default ``STDOUT_FILENO``, or standard
+   output) specifies which file descriptor should be queried.
+
+   If the file descriptor is not connected to a terminal, an :exc:`OSError`
+   is thrown.
+
+   :func:`shutil.get_terminal_size` is the high-level function which
+   should normally be used, ``os.get_terminal_size`` is the low-level
+   implementation.
+
+   Availability: Unix, Windows.
+
+.. class:: terminal_size(tuple)
+
+   A tuple of ``(columns, lines)`` for holding terminal window size.
+
+   .. attribute:: columns
+
+      Width of the terminal window in characters.
+
+   .. attribute:: lines
+
+      Height of the terminal window in characters.
+
+
 .. _os-file-dir:
 
 Files and Directories

Doc/library/shutil.rst

@@ -459,3 +459,36 @@ The resulting archive contains::
     -rw------- tarek/staff    1675 2008-06-09 13:26:54 ./id_rsa
     -rw-r--r-- tarek/staff     397 2008-06-09 13:26:54 ./id_rsa.pub
     -rw-r--r-- tarek/staff   37192 2010-02-06 18:23:10 ./known_hosts
+
+
+Querying the size of the output terminal
+----------------------------------------
+
+.. versionadded:: 3.3
+
+.. function:: get_terminal_size(fallback=(columns, lines))
+
+   Get the size of the terminal window.
+
+   For each of the two dimensions, the environment variable, ``COLUMNS``
+   and ``LINES`` respectively, is checked. If the variable is defined and
+   the value is a positive integer, it is used.
+
+   When ``COLUMNS`` or ``LINES`` is not defined, which is the common case,
+   the terminal connected to :data:`sys.__stdout__` is queried
+   by invoking :func:`os.get_terminal_size`.
+
+   If the terminal size cannot be successfully queried, either because
+   the system doesn't support querying, or because we are not
+   connected to a terminal, the value given in ``fallback`` parameter
+   is used. ``fallback`` defaults to ``(80, 24)`` which is the default
+   size used by many terminal emulators.
+
+   The value returned is a named tuple of type :class:`os.terminal_size`.
+
+   See also: The Single UNIX Specification, Version 2,
+   `Other Environment Variables`_.
+
+.. _`Other Environment Variables`:
+   http://pubs.opengroup.org/onlinepubs/7908799/xbd/envvar.html#tag_002_003
+

Lib/shutil.py

@@ -878,3 +878,46 @@ def chown(path, user=None, group=None):
             raise LookupError("no such group: {!r}".format(group))
 
     os.chown(path, _user, _group)
+
+def get_terminal_size(fallback=(80, 24)):
+    """Get the size of the terminal window.
+
+    For each of the two dimensions, the environment variable, COLUMNS
+    and LINES respectively, is checked. If the variable is defined and
+    the value is a positive integer, it is used.
+
+    When COLUMNS or LINES is not defined, which is the common case,
+    the terminal connected to sys.__stdout__ is queried
+    by invoking os.get_terminal_size.
+
+    If the terminal size cannot be successfully queried, either because
+    the system doesn't support querying, or because we are not
+    connected to a terminal, the value given in fallback parameter
+    is used. Fallback defaults to (80, 24) which is the default
+    size used by many terminal emulators.
+
+    The value returned is a named tuple of type os.terminal_size.
+    """
+    # columns, lines are the working values
+    try:
+        columns = int(os.environ['COLUMNS'])
+    except (KeyError, ValueError):
+        columns = 0
+
+    try:
+        lines = int(os.environ['LINES'])
+    except (KeyError, ValueError):
+        lines = 0
+
+    # only query if necessary
+    if columns <= 0 or lines <= 0:
+        try:
+            size = os.get_terminal_size(sys.__stdout__.fileno())
+        except (NameError, OSError):
+            size = os.terminal_size(fallback)
+        if columns <= 0:
+            columns = size.columns
+        if lines <= 0:
+            lines = size.lines
+
+    return os.terminal_size((columns, lines))

Lib/test/test_os.py

@@ -1840,6 +1840,43 @@ def test_symlink(self):
                               os.symlink, filename, filename)
 
 
+@unittest.skipUnless(hasattr(os, 'get_terminal_size'), "requires os.get_terminal_size")
+class TermsizeTests(unittest.TestCase):
+    def test_does_not_crash(self):
+        """Check if get_terminal_size() returns a meaningful value.
+
+        There's no easy portable way to actually check the size of the
+        terminal, so let's check if it returns something sensible instead.
+        """
+        try:
+            size = os.get_terminal_size()
+        except OSError as e:
+            if e.errno == errno.EINVAL or sys.platform == "win32":
+                # Under win32 a generic OSError can be thrown if the
+                # handle cannot be retrieved
+                self.skipTest("failed to query terminal size")
+            raise
+
+        self.assertGreater(size.columns, 0)
+        self.assertGreater(size.lines, 0)
+
+    def test_stty_match(self):
+        """Check if stty returns the same results
+
+        stty actually tests stdin, so get_terminal_size is invoked on
+        stdin explicitly. If stty succeeded, then get_terminal_size()
+        should work too.
+        """
+        try:
+            size = subprocess.check_output(['stty', 'size']).decode().split()
+        except (FileNotFoundError, subprocess.CalledProcessError):
+            self.skipTest("stty invocation failed")
+        expected = (int(size[1]), int(size[0])) # reversed order
+
+        actual = os.get_terminal_size(sys.__stdin__.fileno())
+        self.assertEqual(expected, actual)
+
+
 @support.reap_threads
 def test_main():
     support.run_unittest(
@@ -1866,6 +1903,7 @@ def test_main():
         ProgramPriorityTests,
         ExtendedAttributeTests,
         Win32DeprecatedBytesAPI,
+        TermsizeTests,
     )
 
 if __name__ == "__main__":

Lib/test/test_shutil.py

@@ -9,6 +9,7 @@
 import os.path
 import errno
 import functools
+import subprocess
 from test import support
 from test.support import TESTFN
 from os.path import splitdrive
@@ -1267,10 +1268,55 @@ def test_move_dir_caseinsensitive(self):
         finally:
             os.rmdir(dst_dir)
 
+class TermsizeTests(unittest.TestCase):
+    def test_does_not_crash(self):
+        """Check if get_terminal_size() returns a meaningful value.
+
+        There's no easy portable way to actually check the size of the
+        terminal, so let's check if it returns something sensible instead.
+        """
+        size = shutil.get_terminal_size()
+        self.assertGreater(size.columns, 0)
+        self.assertGreater(size.lines, 0)
+
+    def test_os_environ_first(self):
+        "Check if environment variables have precedence"
+
+        with support.EnvironmentVarGuard() as env:
+            env['COLUMNS'] = '777'
+            size = shutil.get_terminal_size()
+        self.assertEqual(size.columns, 777)
+
+        with support.EnvironmentVarGuard() as env:
+            env['LINES'] = '888'
+            size = shutil.get_terminal_size()
+        self.assertEqual(size.lines, 888)
+
+    @unittest.skipUnless(os.isatty(sys.__stdout__.fileno()), "not on tty")
+    def test_stty_match(self):
+        """Check if stty returns the same results ignoring env
+
+        This test will fail if stdin and stdout are connected to
+        different terminals with different sizes. Nevertheless, such
+        situations should be pretty rare.
+        """
+        try:
+            size = subprocess.check_output(['stty', 'size']).decode().split()
+        except (FileNotFoundError, subprocess.CalledProcessError):
+            self.skipTest("stty invocation failed")
+        expected = (int(size[1]), int(size[0])) # reversed order
+
+        with support.EnvironmentVarGuard() as env:
+            del env['LINES']
+            del env['COLUMNS']
+            actual = shutil.get_terminal_size()
+
+        self.assertEqual(expected, actual)
 
 
 def test_main():
-    support.run_unittest(TestShutil, TestMove, TestCopyFile)
+    support.run_unittest(TestShutil, TestMove, TestCopyFile,
+                         TermsizeTests)
 
 if __name__ == '__main__':
     test_main()

Misc/NEWS

@@ -466,6 +466,10 @@ Core and Builtins
 Library
 -------
 
+- Issue #13609: Add two functions to query the terminal size:
+  os.get_terminal_size (low level) and shutil.get_terminal_size (high level).
+  Patch by Zbigniew Jędrzejewski-Szmek.
+
 - Issue #13845: On Windows, time.time() now uses GetSystemTimeAsFileTime()
   instead of ftime() to have a resolution of 100 ns instead of 1 ms (the clock
   accuracy is between 0.5 ms and 15 ms).