Add `-N` parameter to `ls` command.

`ls -N` will display one 'screen-ful' of lines (the number of lines in the
console, less 2).

test/data/ListCommand_50_items.txt

+(A) item 1
+(B) item 2
+(C) item 3
+(D) item 4
+(E) item 5
+(F) item 6
+(G) item 7
+(H) item 8
+(I) item 9
+(J) item 10
+(K) item 11
+(L) item 12
+(M) item 13
+(N) item 14
+(O) item 15
+(P) item 16
+(Q) item 17
+(R) item 18
+(S) item 19
+(T) item 20
+(U) item 21
+(V) item 22
+(W) item 23
+(X) item 24
+(Y) item 25
+(Z) item 26
+(A) item 27
+(B) item 28
+(C) item 29
+(D) item 30
+(E) item 31
+(F) item 32
+(G) item 33
+(H) item 34
+(I) item 35
+(J) item 36
+(K) item 37
+(L) item 38
+(M) item 39
+(N) item 40
+(O) item 41
+(P) item 42
+(Q) item 43
+(R) item 44
+(S) item 45
+(T) item 46
+(U) item 47
+(V) item 48
+(W) item 49
+(X) item 50

test/test_list_command.py

@@ -17,6 +17,8 @@
 import codecs
 import re
 import unittest
+from collections import namedtuple
+from unittest import mock
 
 from test.command_testcase import CommandTest
 from test.facilities import load_file_to_todolist
@@ -28,6 +30,7 @@ class ListCommandTest(CommandTest):
     def setUp(self):
         super(ListCommandTest, self).setUp()
         self.todolist = load_file_to_todolist("test/data/ListCommandTest.txt")
+        self.terminal_size = namedtuple('terminal_size', ['columns', 'lines'])
 
     def test_list01(self):
         command = ListCommand([""], self.todolist, self.out, self.error)
@@ -313,13 +316,62 @@ class ListCommandTest(CommandTest):
         self.assertEqual(self.errors, "option -z not recognized\n")
 
     def test_list42(self):
-        command = ListCommand(["-x", "+Project1", "-id:1"], self.todolist, self.out,
-            self.error)
+        command = ListCommand(["-x", "+Project1", "-id:1"], self.todolist,
+                              self.out, self.error)
         command.execute()
 
         self.assertEqual(self.output, "|  1| (C) 2015-11-05 Foo @Context2 Not@Context +Project1 Not+Project\n")
         self.assertEqual(self.errors, "")
 
+    def test_list43(self):
+        """Test basic 'N' parameter."""
+        command = ListCommand(["-N"], self.todolist, self.out, self.error)
+        command.execute()
+
+        self.assertEqual(self.output, "|  1| (C) 2015-11-05 Foo @Context2 Not@Context +Project1 Not+Project\n|  4| (C) Drink beer @ home\n|  5| (C) 13 + 29 = 42\n|  2| (D) Bar @Context1 +Project2\n")
+        self.assertEqual(self.errors, "")
+
+    @mock.patch('topydo.commands.ListCommand.get_terminal_size')
+    def test_list44(self, mock_terminal_size):
+        """
+        Test 'N' parameter with output longer than available terminal lines.
+        """
+        self.todolist = load_file_to_todolist("test/data/ListCommand_50_items.txt")
+        mock_terminal_size.return_value = self.terminal_size(80, 23)
+
+        command = ListCommand(["-N"], self.todolist, self.out, self.error)
+        command.execute()
+
+        self.assertEqual(self.output, "|  1| (A) item 1\n| 27| (A) item 27\n|  2| (B) item 2\n| 28| (B) item 28\n|  3| (C) item 3\n| 29| (C) item 29\n|  4| (D) item 4\n| 30| (D) item 30\n|  5| (E) item 5\n| 31| (E) item 31\n|  6| (F) item 6\n| 32| (F) item 32\n|  7| (G) item 7\n| 33| (G) item 33\n|  8| (H) item 8\n| 34| (H) item 34\n|  9| (I) item 9\n| 35| (I) item 35\n| 10| (J) item 10\n| 36| (J) item 36\n| 11| (K) item 11\n")
+        self.assertEqual(self.errors, "")
+
+    @mock.patch('topydo.commands.ListCommand.get_terminal_size')
+    def test_list45(self, mock_terminal_size):
+        """Test basic 'N' parameter with nine line terminal."""
+        # have 9 lines on the terminal will print 7 items and leave 2 lines
+        # for the next prompt
+        mock_terminal_size.return_value = self.terminal_size(100, 9)
+        self.todolist = load_file_to_todolist("test/data/ListCommand_50_items.txt")
+
+        command = ListCommand(["-N"], self.todolist, self.out, self.error)
+        command.execute()
+
+        self.assertEqual(self.output, "|  1| (A) item 1\n| 27| (A) item 27\n|  2| (B) item 2\n| 28| (B) item 28\n|  3| (C) item 3\n| 29| (C) item 29\n|  4| (D) item 4\n")
+        self.assertEqual(self.errors, "")
+
+    @mock.patch('topydo.commands.ListCommand.get_terminal_size')
+    def test_list46(self, mock_terminal_size):
+        """Test basic 'N' parameter with zero height terminal."""
+        # we still print at least 1 item
+        mock_terminal_size.return_value = self.terminal_size(100, 0)
+        self.todolist = load_file_to_todolist("test/data/ListCommand_50_items.txt")
+
+        command = ListCommand(["-N"], self.todolist, self.out, self.error)
+        command.execute()
+
+        self.assertEqual(self.output, "|  1| (A) item 1\n")
+        self.assertEqual(self.errors, "")
+
     def test_help(self):
         command = ListCommand(["help"], self.todolist, self.out, self.error)
         command.execute()

topydo/commands/ListCommand.py

@@ -20,6 +20,7 @@ from topydo.lib.Filter import InstanceFilter
 from topydo.lib.PrettyPrinter import pretty_printer_factory
 from topydo.lib.prettyprinters.Format import PrettyPrinterFormatFilter
 from topydo.lib.TodoListBase import InvalidTodoException
+from topydo.lib.Utils import get_terminal_size
 
 
 class ListCommand(ExpressionCommand):
@@ -50,7 +51,7 @@ class ListCommand(ExpressionCommand):
         return True
 
     def _process_flags(self):
-        opts, args = self.getopt('f:F:i:n:s:x')
+        opts, args = self.getopt('f:F:i:n:Ns:x')
 
         for opt, value in opts:
             if opt == '-x':
@@ -69,6 +70,10 @@ class ListCommand(ExpressionCommand):
                     self.printer = None
             elif opt == '-F':
                 self.format = value
+            elif opt == '-N':
+                # 2 lines are assumed to be taken up by printing the next prompt
+                # display at least one item
+                self.limit = max(get_terminal_size().lines - 2, 1)
             elif opt == '-n':
                 try:
                     self.limit = int(value)
@@ -142,7 +147,7 @@ class ListCommand(ExpressionCommand):
 
     def usage(self):
         return """Synopsis: ls [-x] [-s <sort_expression>] [-f <output format>]
-[-F <format string>] [-i <item numbers>] [-n <integer>] [expression]"""
+[-F <format string>] [-i <item numbers>] [-N | -n <integer>] [expression]"""
 
     def help(self):
         return """\
@@ -195,6 +200,7 @@ When an expression is given, only the todos matching that expression are shown.
      A tab character serves as a marker to start right alignment.
 -i : Comma separated list of todo IDs to print.
 -n : Number of items to display. Defaults to the value in the configuration.
+-N : Limit number of items displayed such that they fit on the terminal.
 -s : Sort the list according to a sort expression. Defaults to the expression
      in the configuration.
 -x : Show all todos (i.e. do not filter on dependencies or relevance).