📝 Update boolean values

Author: veit

docs/appendix/checks.rst

@@ -109,12 +109,24 @@ Checks
 
 * Decide whether the following statements are true or false:
 
-  * ``1`` → True
-  * ``0`` → False
-  * ``-1`` → True
-  * ``[0]`` → True (List with one task)
-  * ``1 and 0`` → False
-  * ``1 > 0 or []`` → True
+  .. code-block:: console
+
+     >>> bool([0])
+     True
+     >>> bool(1)
+     True
+     bool(0)
+     False
+     >>> bool(-1)
+     True
+     >>> bool([0])  # Liste mit einem Element
+     True
+     >>> bool([])   # Liste mit keinem Element
+     False
+     >>> bool(1 and 0)
+     False
+     >>> bool(1 > 0 or [])
+     True
 
 :doc:`/types/sequences-sets/lists`
 ----------------------------------

docs/oop/types.rst

@@ -89,9 +89,14 @@ example with a simple inheritance hierarchy makes this clearer:
    :func:`python3:isinstance`
         determines whether, for example, a class passed to a function or method
         is of the expected type.
+
+   .. start-issubclass
+
    :func:`python3:issubclass`
         determines whether one class is the subclass of another.
 
+   .. end-issubclass
+
    .. code-block:: pycon
 
       >>> issubclass(Circle, Form)

docs/types/numbers/bool.rst

@@ -1,24 +1,45 @@
 Boolean values
 ==============
 
-Boolean values are used in the following examples:
+Boolean values are integers in Python:
 
 .. code-block:: pycon
 
-    >>> x = False
-    >>> x
-    False
-    >>> not x
-    True
+   >>> issubclass(bool, int)
+   True
+
+.. include:: ../../oop/types.rst
+   :start-after: start-issubclass
+   :end-before: end-issubclass
+
+``True`` behaves like a ``1`` and ``False`` like a ``0``. There are, in fact,
+certain situations in which this is very useful.
+
+The functions :py:func:`any` and :py:func:`all` check whether at least one or
+all elements in an iterable satisfy the respective condition:
+
+.. code-block:: pycon
+
+   >>> numbers = [0, 1, -1, 2, 3]
+   >>> any(n > 0 for n in numbers)
+   True
+   >>> any(n < 0 for n in numbers)
+   True
+   >>> all(n > 0 for n in numbers)
+   False
+   >>> all(n < 0 for n in numbers)
+   False
+
+However, neither ``any`` nor ``all`` can tell you how many elements match. To
+count the number of matches, you can use :py:func:`sum` instead:
 
 .. code-block:: pycon
 
-    >>> y = True * 2
-    >>> y
-    2
+   >>> sum(n > 0 for n in numbers)
+   3
 
-Apart from their representation as ``True`` and ``False``, Boolean values
-behave like the numbers ``1`` (``True``) and ``0`` (``False``).
+This involves counting the number of ``True`` values by adding together ``True``
+and ``False``.
 
 Checks
 ------
@@ -29,5 +50,6 @@ Checks
   * ``0``
   * ``-1``
   * ``[0]``
+  * ``[]``
   * ``1 and 0``
   * ``1 > 0 or []``