Make padding of IDs dependent of todo list length

When using numerical IDs, the ID width is padded to the log10 of the
todo length.

When using textual IDs, todo lists of 466 items or shorter pad to 3
characters, otherwise 4 characters.

topydo/lib/ListFormat.py

@@ -162,9 +162,9 @@ class ListFormatParser(object):
             # todo ID
             'i': lambda t: str(self.todolist.number(t)),
 
-            # todo ID pre-filled with 1 or 2 spaces if its length is <3
-            'I': lambda t: _filler(str(self.todolist.number(t)), 3),
-
+            # todo ID, padded with spaces
+            'I': lambda t: _filler(str(self.todolist.number(t)),
+                self.todolist.max_id_length()),
 
             # list of tags (spaces) without hidden ones and due: and t:
             'k': lambda t: ' '.join([u'{}:{}'.format(tag, value)
@@ -179,8 +179,9 @@ class ListFormatParser(object):
             # line number
             'n': lambda t: str(self.todolist.linenumber(t)),
 
-            # line number, pre-filled with 1 or 2 spaces if its length <3
-            'N': lambda t: _filler(str(self.todolist.linenumber(t)), 3),
+            # line number, padded with spaces
+            'N': lambda t: _filler(str(self.todolist.linenumber(t)),
+                self.todolist.max_id_length()),
 
             # priority
             'p': lambda t: t.priority() if t.priority() else '',
@@ -206,8 +207,9 @@ class ListFormatParser(object):
             # unique text ID
             'u': lambda t: self.todolist.uid(t),
 
-            # unique text ID, pre-filled with 1 or 2 spaces if its length <3
-            'U': lambda t: _filler(self.todolist.uid(t), 3),
+            # unique text ID, padded with spaces
+            'U': lambda t: _filler(self.todolist.uid(t),
+                self.todolist.max_id_length()),
 
             # absolute completion date
             'x': lambda t: 'x ' + t.completion_date().isoformat() if t.is_completed() else '',

topydo/lib/TodoListBase.py

@@ -18,12 +18,13 @@
 A list of todo items.
 """
 
+import math
 import re
 from datetime import date
 
 from topydo.lib import Filter
 from topydo.lib.Config import config
-from topydo.lib.HashListValues import hash_list_values
+from topydo.lib.HashListValues import hash_list_values, max_id_length
 from topydo.lib.printers.PrettyPrinter import PrettyPrinter
 from topydo.lib.Todo import Todo
 from topydo.lib.View import View
@@ -275,6 +276,19 @@ class TodoListBase(object):
         else:
             return self.linenumber(p_todo)
 
+    def max_id_length(self):
+        """
+        Returns the maximum length of a todo ID, used for formatting purposes.
+        """
+        if config().identifiers() == "text":
+            return max_id_length(len(self._todos))
+        else:
+            try:
+                return math.ceil(math.log(len(self._todos), 10))
+            except ValueError:
+                return 0
+
+
     def _update_todo_ids(self):
         # the idea is to have a hash that is independent of the position of the
         # todo. Use the text (without tags) of the todo to keep the id as