Add doctests (GH-25474)

Doc/howto/sorting.rst

@@ -18,7 +18,9 @@ Sorting Basics
 ==============
 
 A simple ascending sort is very easy: just call the :func:`sorted` function. It
-returns a new sorted list::
+returns a new sorted list:
+
+.. doctest::
 
     >>> sorted([5, 2, 3, 1, 4])
     [1, 2, 3, 4, 5]
@@ -28,6 +30,8 @@ in-place (and returns ``None`` to avoid confusion). Usually it's less convenient
 than :func:`sorted` - but if you don't need the original list, it's slightly
 more efficient.
 
+.. doctest::
+
     >>> a = [5, 2, 3, 1, 4]
     >>> a.sort()
     >>> a
@@ -36,6 +40,8 @@ more efficient.
 Another difference is that the :meth:`list.sort` method is only defined for
 lists. In contrast, the :func:`sorted` function accepts any iterable.
 
+.. doctest::
+
     >>> sorted({1: 'D', 2: 'B', 3: 'B', 4: 'E', 5: 'A'})
     [1, 2, 3, 4, 5]
 
@@ -48,6 +54,8 @@ comparisons.
 
 For example, here's a case-insensitive string comparison:
 
+.. doctest::
+
     >>> sorted("This is a test string from Andrew".split(), key=str.lower)
     ['a', 'Andrew', 'from', 'is', 'string', 'test', 'This']
 
@@ -59,6 +67,8 @@ input record.
 A common pattern is to sort complex objects using some of the object's indices
 as keys. For example:
 
+.. doctest::
+
     >>> student_tuples = [
     ...     ('john', 'A', 15),
     ...     ('jane', 'B', 12),
@@ -69,6 +79,8 @@ as keys. For example:
 
 The same technique works for objects with named attributes. For example:
 
+.. doctest::
+
     >>> class Student:
     ...     def __init__(self, name, grade, age):
     ...         self.name = name
@@ -95,6 +107,8 @@ convenience functions to make accessor functions easier and faster. The
 
 Using those functions, the above examples become simpler and faster:
 
+.. doctest::
+
     >>> from operator import itemgetter, attrgetter
 
     >>> sorted(student_tuples, key=itemgetter(2))
@@ -106,6 +120,8 @@ Using those functions, the above examples become simpler and faster:
 The operator module functions allow multiple levels of sorting. For example, to
 sort by *grade* then by *age*:
 
+.. doctest::
+
     >>> sorted(student_tuples, key=itemgetter(1,2))
     [('john', 'A', 15), ('dave', 'B', 10), ('jane', 'B', 12)]
 
@@ -119,6 +135,8 @@ Both :meth:`list.sort` and :func:`sorted` accept a *reverse* parameter with a
 boolean value. This is used to flag descending sorts. For example, to get the
 student data in reverse *age* order:
 
+.. doctest::
+
     >>> sorted(student_tuples, key=itemgetter(2), reverse=True)
     [('john', 'A', 15), ('jane', 'B', 12), ('dave', 'B', 10)]
 
@@ -132,6 +150,8 @@ Sorts are guaranteed to be `stable
 <https://en.wikipedia.org/wiki/Sorting_algorithm#Stability>`_\. That means that
 when multiple records have the same key, their original order is preserved.
 
+.. doctest::
+
     >>> data = [('red', 1), ('blue', 1), ('red', 2), ('blue', 2)]
     >>> sorted(data, key=itemgetter(0))
     [('blue', 1), ('blue', 2), ('red', 1), ('red', 2)]
@@ -143,6 +163,8 @@ This wonderful property lets you build complex sorts in a series of sorting
 steps. For example, to sort the student data by descending *grade* and then
 ascending *age*, do the *age* sort first and then sort again using *grade*:
 
+.. doctest::
+
     >>> s = sorted(student_objects, key=attrgetter('age'))     # sort on secondary key
     >>> sorted(s, key=attrgetter('grade'), reverse=True)       # now sort on primary key, descending
     [('dave', 'B', 10), ('jane', 'B', 12), ('john', 'A', 15)]
@@ -150,6 +172,8 @@ ascending *age*, do the *age* sort first and then sort again using *grade*:
 This can be abstracted out into a wrapper function that can take a list and
 tuples of field and order to sort them on multiple passes.
 
+.. doctest::
+
     >>> def multisort(xs, specs):
     ...     for key, reverse in reversed(specs):
     ...         xs.sort(key=attrgetter(key), reverse=reverse)
@@ -220,6 +244,8 @@ comparisons. That function should take two arguments to be compared and then
 return a negative value for less-than, return zero if they are equal, or return
 a positive value for greater-than. For example, we can do:
 
+.. doctest::
+
     >>> def numeric_compare(x, y):
     ...     return x - y
     >>> sorted([5, 2, 4, 1, 3], cmp=numeric_compare) # doctest: +SKIP
@@ -227,6 +253,8 @@ a positive value for greater-than. For example, we can do:
 
 Or you can reverse the order of comparison with:
 
+.. doctest::
+
     >>> def reverse_numeric(x, y):
     ...     return y - x
     >>> sorted([5, 2, 4, 1, 3], cmp=reverse_numeric) # doctest: +SKIP
@@ -234,7 +262,9 @@ Or you can reverse the order of comparison with:
 
 When porting code from Python 2.x to 3.x, the situation can arise when you have
 the user supplying a comparison function and you need to convert that to a key
-function. The following wrapper makes that easy to do::
+function. The following wrapper makes that easy to do:
+
+.. testcode::
 
     def cmp_to_key(mycmp):
         'Convert a cmp= function into a key= function'
@@ -255,6 +285,12 @@ function. The following wrapper makes that easy to do::
                 return mycmp(self.obj, other.obj) != 0
         return K
 
+.. doctest::
+    :hide:
+
+    >>> sorted([5, 2, 4, 1, 3], key=cmp_to_key(reverse_numeric))
+    [5, 4, 3, 2, 1]
+
 To convert to a key function, just wrap the old comparison function:
 
 .. testsetup::
@@ -280,6 +316,8 @@ Odd and Ends
   simulated without the parameter by using the builtin :func:`reversed` function
   twice:
 
+  .. doctest::
+
     >>> data = [('red', 1), ('blue', 1), ('red', 2), ('blue', 2)]
     >>> standard_way = sorted(data, key=itemgetter(0), reverse=True)
     >>> double_reversed = list(reversed(sorted(reversed(data), key=itemgetter(0))))
@@ -289,7 +327,9 @@ Odd and Ends
 
 * The sort routines are guaranteed to use :meth:`__lt__` when making comparisons
   between two objects. So, it is easy to add a standard sort order to a class by
-  defining an :meth:`__lt__` method::
+  defining an :meth:`__lt__` method:
+
+  .. doctest::
 
     >>> Student.__lt__ = lambda self, other: self.age < other.age
     >>> sorted(student_objects)
@@ -300,6 +340,8 @@ Odd and Ends
   are stored in a dictionary, they can be used to sort a separate list of student
   names:
 
+  .. doctest::
+
     >>> students = ['dave', 'john', 'jane']
     >>> newgrades = {'john': 'F', 'jane':'A', 'dave': 'C'}
     >>> sorted(students, key=newgrades.__getitem__)