Document another recipe for itertools: all_equal(). Inspired by David Beazley.

rhettinger · rhettinger · commit e525ee3b4838 · 2016-03-06T18:11:38.000-08:00
diff --git a/Doc/library/itertools.rst b/Doc/library/itertools.rst
@@ -693,6 +693,11 @@ which incur interpreter overhead.
        "Returns the nth item or a default value"
        return next(islice(iterable, n, None), default)
 
+   def all_equal(iterable):
+       "Returns True if all the elements are equal to each other"
+       g = groupby(iterable)
+       return next(g, True) and not next(g, False)
+
    def quantify(iterable, pred=bool):
        "Count how many times the predicate is true"
        return sum(map(pred, iterable))
diff --git a/Lib/test/test_itertools.py b/Lib/test/test_itertools.py
@@ -2014,6 +2014,11 @@ def test_permutations_sizeof(self):
 ...     "Returns the nth item or a default value"
 ...     return next(islice(iterable, n, None), default)
 
+>>> def all_equal(iterable):
+...     "Returns True if all the elements are equal to each other"
+...     g = groupby(iterable)
+...     return next(g, True) and not next(g, False)
+
 >>> def quantify(iterable, pred=bool):
 ...     "Count how many times the predicate is true"
 ...     return sum(map(pred, iterable))
@@ -2127,6 +2132,9 @@ def test_permutations_sizeof(self):
 >>> nth('abcde', 9) is None
 True
 
+>>> [all_equal(s) for s in ('', 'A', 'AAAA', 'AAAB', 'AAABA')]
+[True, True, True, False, False]
+
 >>> quantify(range(99), lambda x: x%2==0)
 50
 
