diff -r 90681462f16a Lib/timeit.py
--- a/Lib/timeit.py	Wed Sep 21 14:14:59 2016 +0200
+++ b/Lib/timeit.py	Wed Sep 21 15:59:40 2016 +0200
@@ -50,7 +50,6 @@ Functions:
 
 """
 
-import gc
 import sys
 import time
 import itertools
@@ -59,7 +58,7 @@ import itertools
 
 dummy_src_name = "<timeit-src>"
 default_number = 1000000
-default_repeat = 3
+default_repeat = 5
 default_timer = time.perf_counter
 
 _globals = globals
@@ -172,13 +171,7 @@ class Timer:
         the timer function to be used are passed to the constructor.
         """
         it = itertools.repeat(None, number)
-        gcold = gc.isenabled()
-        gc.disable()
-        try:
-            timing = self.inner(it, self.timer)
-        finally:
-            if gcold:
-                gc.enable()
+        timing = self.inner(it, self.timer)
         return timing
 
     def repeat(self, repeat=default_repeat, number=default_number):
@@ -218,7 +211,7 @@ class Timer:
         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(1, 10):
+        for i in range(0, 10):
             number = 10**i
             time_taken = self.timeit(number)
             if callback:
@@ -237,6 +230,23 @@ def repeat(stmt="pass", setup="pass", ti
     """Convenience function to create Timer object and call repeat method."""
     return Timer(stmt, setup, timer, globals).repeat(repeat, number)
 
+
+def _format_loops(number):
+    r = 1
+    if number >= 10_000:
+        x = number
+        pow10 = 0
+        while x >= 10:
+            x, r = divmod(x, 10)
+            pow10 += 1
+            if r:
+                break
+
+    if not r:
+        return '10^%s' % pow10
+    else:
+        return str(number)
+
 def main(args=None, *, _wrap_timer=None):
     """Main program, used when run as a script.
 
@@ -256,7 +266,10 @@ def main(args=None, *, _wrap_timer=None)
     """
     if args is None:
         args = sys.argv[1:]
+
     import getopt
+    import statistics
+
     try:
         opts, args = getopt.getopt(args, "n:u:s:r:tcpvh",
                                    ["number=", "setup=", "repeat=",
@@ -266,6 +279,7 @@ def main(args=None, *, _wrap_timer=None)
         print(err)
         print("use -h/--help for command line help")
         return 2
+
     timer = default_timer
     stmt = "\n".join(args) or "pass"
     number = 0 # auto-determine
@@ -273,19 +287,26 @@ def main(args=None, *, _wrap_timer=None)
     repeat = default_repeat
     verbose = 0
     time_unit = None
-    units = {"usec": 1, "msec": 1e3, "sec": 1e6}
+    units = {"sec": 1, "msec": 1e3, "usec": 1e6, "ns": 1e9}
     precision = 3
     for o, a in opts:
         if o in ("-n", "--number"):
-            number = int(a)
+            if '^' in a:
+                number, _, power = a.partition('^')
+                number = int(number)
+                power = int(power)
+                number = number ** power
+            else:
+                number = int(a)
         if o in ("-s", "--setup"):
             setup.append(a)
         if o in ("-u", "--unit"):
             if a in units:
                 time_unit = a
             else:
-                print("Unrecognized unit. Please select usec, msec, or sec.",
-                    file=sys.stderr)
+                print("Unrecognized unit. Please select: %s"
+                      % ', '.join(units),
+                      file=sys.stderr)
                 return 2
         if o in ("-r", "--repeat"):
             repeat = int(a)
@@ -304,6 +325,7 @@ def main(args=None, *, _wrap_timer=None)
         if o in ("-h", "--help"):
             print(__doc__, end=' ')
             return 0
+
     setup = "\n".join(setup) or "pass"
     # Include the current directory, so that local imports work (sys.path
     # contains the directory of this script, rather than the current
@@ -319,43 +341,49 @@ def main(args=None, *, _wrap_timer=None)
         if verbose:
             def callback(number, time_taken):
                 msg = "{num} loops -> {secs:.{prec}g} secs"
-                print(msg.format(num=number, secs=time_taken, prec=precision))
+                print(msg.format(num=_format_loops(number),
+                                 secs=time_taken, prec=precision))
         try:
             number, _ = t.autorange(callback)
         except:
             t.print_exc()
             return 1
+
     try:
-        r = t.repeat(repeat, number)
+        timings = t.repeat(repeat, number)
     except:
         t.print_exc()
         return 1
-    best = min(r)
+
     if verbose:
-        print("raw times:", " ".join(["%.*g" % (precision, x) for x in r]))
-    print("%d loops," % number, end=' ')
-    usec = best * 1e6 / number
+        raw_times = ", ".join("%.*g sec" % (precision, x) for x in timings)
+        print("raw times: %s" % raw_times)
+
+    timings = [dt / number for dt in timings]
+
+    average = sum(timings) / len(timings)
     if time_unit is not None:
         scale = units[time_unit]
     else:
         scales = [(scale, unit) for unit, scale in units.items()]
-        scales.sort(reverse=True)
+        scales.sort()
         for scale, time_unit in scales:
-            if usec >= scale:
+            if average * scale >= 1.0:
                 break
-    print("best of %d: %.*g %s per loop" % (repeat, precision,
-                                            usec/scale, time_unit))
-    best = min(r)
-    usec = best * 1e6 / number
-    worst = max(r)
+
+    stdev = statistics.stdev(timings, average)
+    print("%s loops, average of %d: %.*g %s +- %.*g %s per loop"
+          % (_format_loops(number), repeat,
+             precision, average * scale, time_unit,
+             precision, stdev * scale, time_unit))
+    best = min(timings)
+    worst = max(timings)
     if worst >= best * 4:
-        usec = worst * 1e6 / number
-        import warnings
-        warnings.warn_explicit(
-            "The test results are likely unreliable. The worst\n"
-            "time (%.*g %s) was more than four times slower than the best time." %
-            (precision, usec/scale, time_unit),
-             UserWarning, '', 0)
+        print("WARNING: The test results are likely unreliable. "
+              "The worst time (%.*g %s) was more than four times slower than "
+              "the best time (%.*g %s)."
+              % (precision, worst * scale, time_unit,
+                 precision, best * scale, time_unit))
     return None
 
 if __name__ == "__main__":