Issue #28469: timeit now uses the sequence 1, 2, 5, 10, 20, 50,... instead

of 1, 10, 100,... for autoranging.

Doc/library/timeit.rst

@@ -28,11 +28,11 @@ can be used to compare three different expressions:
 .. code-block:: sh
 
    $ python3 -m timeit '"-".join(str(n) for n in range(100))'
-   10000 loops, best of 3: 30.2 usec per loop
+   10000 loops, best of 5: 30.2 usec per loop
    $ python3 -m timeit '"-".join([str(n) for n in range(100)])'
-   10000 loops, best of 3: 27.5 usec per loop
+   10000 loops, best of 5: 27.5 usec per loop
    $ python3 -m timeit '"-".join(map(str, range(100)))'
-   10000 loops, best of 3: 23.2 usec per loop
+   10000 loops, best of 5: 23.2 usec per loop
 
 This can be achieved from the :ref:`python-interface` with::
 
@@ -141,9 +141,8 @@ The module defines three convenience functions and a public class:
        This is a convenience function that calls :meth:`.timeit` repeatedly
        so that the total time >= 0.2 second, returning the eventual
        (number of loops, time taken for that number of loops). It calls
-       :meth:`.timeit` with *number* set to successive powers of ten (10,
-       100, 1000, ...) up to a maximum of one billion, until the time taken
-       is at least 0.2 second, or the maximum is reached.
+       :meth:`.timeit` with increasing numbers from the sequence 1, 2, 5,
+       10, 20, 50, ... until the time taken is at least 0.2 second.
 
         If *callback* is given and is not ``None``, it will be called after
         each trial with two arguments: ``callback(number, time_taken)``.
@@ -268,9 +267,9 @@ It is possible to provide a setup statement that is executed only once at the be
 .. code-block:: sh
 
    $ python -m timeit -s 'text = "sample string"; char = "g"'  'char in text'
-   10000000 loops, best of 3: 0.0877 usec per loop
+   5000000 loops, best of 5: 0.0877 usec per loop
    $ python -m timeit -s 'text = "sample string"; char = "g"'  'text.find(char)'
-   1000000 loops, best of 3: 0.342 usec per loop
+   1000000 loops, best of 5: 0.342 usec per loop
 
 ::
 
@@ -297,14 +296,14 @@ to test for missing and present object attributes:
 .. code-block:: sh
 
    $ python -m timeit 'try:' '  str.__bool__' 'except AttributeError:' '  pass'
-   100000 loops, best of 3: 15.7 usec per loop
+   20000 loops, best of 5: 15.7 usec per loop
    $ python -m timeit 'if hasattr(str, "__bool__"): pass'
-   100000 loops, best of 3: 4.26 usec per loop
+   50000 loops, best of 5: 4.26 usec per loop
 
    $ python -m timeit 'try:' '  int.__bool__' 'except AttributeError:' '  pass'
-   1000000 loops, best of 3: 1.43 usec per loop
+   200000 loops, best of 5: 1.43 usec per loop
    $ python -m timeit 'if hasattr(int, "__bool__"): pass'
-   100000 loops, best of 3: 2.23 usec per loop
+   100000 loops, best of 5: 2.23 usec per loop
 
 ::
 

Lib/test/test_timeit.py

@@ -256,7 +256,7 @@ class TestTimeit(unittest.TestCase):
 
     def test_main_milliseconds(self):
         s = self.run_main(seconds_per_increment=0.0055)
-        self.assertEqual(s, "100 loops, best of 5: 5.5 msec per loop\n")
+        self.assertEqual(s, "50 loops, best of 5: 5.5 msec per loop\n")
 
     def test_main_microseconds(self):
         s = self.run_main(seconds_per_increment=0.0000025, switches=['-n100'])
@@ -304,35 +304,43 @@ class TestTimeit(unittest.TestCase):
             """))
 
     def test_main_very_verbose(self):
-        s = self.run_main(seconds_per_increment=0.000050, switches=['-vv'])
+        s = self.run_main(seconds_per_increment=0.000_030, switches=['-vv'])
         self.assertEqual(s, dedent("""\
-                1 loop -> 5e-05 secs
-                10 loops -> 0.0005 secs
-                100 loops -> 0.005 secs
-                1000 loops -> 0.05 secs
-                10000 loops -> 0.5 secs
-
-                raw times: 500 msec, 500 msec, 500 msec, 500 msec, 500 msec
-
-                10000 loops, best of 5: 50 usec per loop
+                1 loop -> 3e-05 secs
+                2 loops -> 6e-05 secs
+                5 loops -> 0.00015 secs
+                10 loops -> 0.0003 secs
+                20 loops -> 0.0006 secs
+                50 loops -> 0.0015 secs
+                100 loops -> 0.003 secs
+                200 loops -> 0.006 secs
+                500 loops -> 0.015 secs
+                1000 loops -> 0.03 secs
+                2000 loops -> 0.06 secs
+                5000 loops -> 0.15 secs
+                10000 loops -> 0.3 secs
+
+                raw times: 300 msec, 300 msec, 300 msec, 300 msec, 300 msec
+
+                10000 loops, best of 5: 30 usec per loop
             """))
 
     def test_main_with_time_unit(self):
-        unit_sec = self.run_main(seconds_per_increment=0.002,
+        unit_sec = self.run_main(seconds_per_increment=0.003,
                 switches=['-u', 'sec'])
         self.assertEqual(unit_sec,
-                "100 loops, best of 5: 0.002 sec per loop\n")
-        unit_msec = self.run_main(seconds_per_increment=0.002,
+                "100 loops, best of 5: 0.003 sec per loop\n")
+        unit_msec = self.run_main(seconds_per_increment=0.003,
                 switches=['-u', 'msec'])
         self.assertEqual(unit_msec,
-                "100 loops, best of 5: 2 msec per loop\n")
-        unit_usec = self.run_main(seconds_per_increment=0.002,
+                "100 loops, best of 5: 3 msec per loop\n")
+        unit_usec = self.run_main(seconds_per_increment=0.003,
                 switches=['-u', 'usec'])
         self.assertEqual(unit_usec,
-                "100 loops, best of 5: 2e+03 usec per loop\n")
+                "100 loops, best of 5: 3e+03 usec per loop\n")
         # Test invalid unit input
         with captured_stderr() as error_stringio:
-            invalid = self.run_main(seconds_per_increment=0.002,
+            invalid = self.run_main(seconds_per_increment=0.003,
                     switches=['-u', 'parsec'])
         self.assertEqual(error_stringio.getvalue(),
                     "Unrecognized unit. Please select nsec, usec, msec, or sec.\n")
@@ -347,15 +355,15 @@ class TestTimeit(unittest.TestCase):
             s = self.run_main(switches=['-n1', '1/0'])
         self.assert_exc_string(error_stringio.getvalue(), 'ZeroDivisionError')
 
-    def autorange(self, seconds_per_increment=0.001, callback=None):
+    def autorange(self, seconds_per_increment=1/1024, callback=None):
         timer = FakeTimer(seconds_per_increment=seconds_per_increment)
         t = timeit.Timer(stmt=self.fake_stmt, setup=self.fake_setup, timer=timer)
         return t.autorange(callback)
 
     def test_autorange(self):
         num_loops, time_taken = self.autorange()
-        self.assertEqual(num_loops, 1000)
-        self.assertEqual(time_taken, 1.0)
+        self.assertEqual(num_loops, 500)
+        self.assertEqual(time_taken, 500/1024)
 
     def test_autorange_second(self):
         num_loops, time_taken = self.autorange(seconds_per_increment=1.0)
@@ -367,12 +375,17 @@ class TestTimeit(unittest.TestCase):
             print("{} {:.3f}".format(a, b))
         with captured_stdout() as s:
             num_loops, time_taken = self.autorange(callback=callback)
-        self.assertEqual(num_loops, 1000)
-        self.assertEqual(time_taken, 1.0)
+        self.assertEqual(num_loops, 500)
+        self.assertEqual(time_taken, 500/1024)
         expected = ('1 0.001\n'
+                    '2 0.002\n'
+                    '5 0.005\n'
                     '10 0.010\n'
-                    '100 0.100\n'
-                    '1000 1.000\n')
+                    '20 0.020\n'
+                    '50 0.049\n'
+                    '100 0.098\n'
+                    '200 0.195\n'
+                    '500 0.488\n')
         self.assertEqual(s.getvalue(), expected)
 
 

Lib/timeit.py

@@ -208,22 +208,23 @@ class Timer:
     def autorange(self, callback=None):
         """Return the number of loops so that total time >= 0.2.
 
-        Calls the timeit method with *number* set to successive powers of
-        ten (10, 100, 1000, ...) up to a maximum of one billion, until
-        the time taken is at least 0.2 second, or the maximum is reached.
-        Returns ``(number, time_taken)``.
+        Calls the timeit method with increasing numbers from the sequence
+        1, 2, 5, 10, 20, 50, ... until the time taken is at least 0.2
+        second.  Returns (number, time_taken).
 
         If *callback* is given and is not None, it will be called after
         each trial with two arguments: ``callback(number, time_taken)``.
         """
-        for i in range(0, 10):
-            number = 10**i
-            time_taken = self.timeit(number)
-            if callback:
-                callback(number, time_taken)
-            if time_taken >= 0.2:
-                break
-        return (number, time_taken)
+        i = 1
+        while True:
+            for j in 1, 2, 5:
+                number = i * j
+                time_taken = self.timeit(number)
+                if callback:
+                    callback(number, time_taken)
+                if time_taken >= 0.2:
+                    return (number, time_taken)
+            i *= 10
 
 def timeit(stmt="pass", setup="pass", timer=default_timer,
            number=default_number, globals=None):

Misc/NEWS

@@ -97,6 +97,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #28469: timeit now uses the sequence 1, 2, 5, 10, 20, 50,... instead
+  of 1, 10, 100,... for autoranging.
+
 - Issue #28115: Command-line interface of the zipfile module now uses argparse.
   Added support of long options.