add allsame: test if all elements of an iterable are the same

Technologicat · Technologicat · commit 8baf00928b26 · 2020-08-20T19:33:04.000+03:00
Checked using `!=`.
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -10,6 +10,7 @@
 - `callsite_filename`: return the filename from which this function is being called. Useful as a building block for debug utilities and similar.
 - `equip_with_traceback`: take a manually created exception instance, equip it with a traceback. Requires Python 3.7 or later.
 - `subset`: test whether an iterable is a subset of another. Convenience function.
+- `allsame`: test whether all elements of an iterable are the same. Sometimes useful in writing testing code.
 
 **Non-breaking changes**:
 
diff --git a/unpythonic/it.py b/unpythonic/it.py
@@ -28,7 +28,8 @@
            "window", "chunked",
            "within", "fixpoint",
            "interleave",
-           "subset", "powerset"]
+           "subset", "powerset",
+           "allsame"]
 
 from builtins import map as stdlib_map
 from operator import itemgetter
@@ -991,3 +992,24 @@ def total_num_items(ld):
         bag.append(x)
         yield from t
         bag.extend(t)
+
+def allsame(iterable):
+    """Return whether all elements of an iterable are the same.
+
+    The test uses `!=` to compare.
+
+    If `iterable` is empty, the return value is `True` (like for `all`).
+
+    If `iterable` has just one element, the return value is `True`.
+
+    **CAUTION**: Consumes consumable iterables.
+    """
+    it = iter(iterable)
+    try:
+        x0 = next(it)
+    except StopIteration:
+        return True  # like all(()) is True
+    for x in it:
+        if x != x0:
+            return False
+    return True
diff --git a/unpythonic/test/test_it.py b/unpythonic/test/test_it.py
@@ -26,7 +26,8 @@
                   window, chunked,
                   within, fixpoint,
                   interleave,
-                  subset, powerset)
+                  subset, powerset,
+                  allsame)
 
 from ..fun import composel, identity, curry
 from ..gmemo import imemoize, gmemoize
@@ -345,6 +346,12 @@ def sqrt_iter(x):  # has an attractive fixed point at sqrt(n)
         test[all(sum(terms) == 10 for terms in partition_int(10, lower=3))]
         test[all(sum(terms) == 10 for terms in partition_int(10, lower=3, upper=5))]
 
+    with testset("allsame"):
+        test[allsame(())]
+        test[allsame((1,))]
+        test[allsame((8, 8, 8, 8, 8))]
+        test[not allsame((1, 2, 3))]
+
 if __name__ == '__main__':  # pragma: no cover
     with session(__file__):
         runtests()
