MaxNLocator only returns points within bounds.

e.g. when the xlims are -0.5 .. 10.5, return 0 .. 10 instead of -1
.. 11.  This implies dropping the (unused and deprecated-in-comment)
"trim" keyword argument.

Also slightly clean up the implementation of scale_range.

Preliminary work on matplotlib#5738.

lib/matplotlib/ticker.py

@@ -161,6 +161,7 @@
 from matplotlib import rcParams
 from matplotlib import cbook
 from matplotlib import transforms as mtransforms
+from matplotlib.cbook import mplDeprecation
 
 import warnings
 
@@ -1323,23 +1324,12 @@ def view_limits(self, dmin, dmax):
 
 
 def scale_range(vmin, vmax, n=1, threshold=100):
-    dv = abs(vmax - vmin)
-    if dv == 0:     # maxabsv == 0 is a special case of this.
-        return 1.0, 0.0
-        # Note: this should never occur because
-        # vmin, vmax should have been checked by nonsingular(),
-        # and spread apart if necessary.
-    meanv = 0.5 * (vmax + vmin)
-    if abs(meanv) / dv < threshold:
-        offset = 0
-    elif meanv > 0:
-        ex = divmod(math.log10(meanv), 1)[0]
-        offset = 10 ** ex
-    else:
-        ex = divmod(math.log10(-meanv), 1)[0]
-        offset = -10 ** ex
-    ex = divmod(math.log10(dv / n), 1)[0]
-    scale = 10 ** ex
+    dv = abs(vmax - vmin) # > 0 as nonsingular is called before.
+    meanv = (vmax + vmin) / 2
+    offset = (math.copysign(10 ** (math.log10(abs(meanv)) // 1), meanv)
+              if abs(meanv) / dv >= threshold
+              else 0)
+    scale = 10 ** (math.log10(dv / n) // 1)
     return scale, offset
 
 
@@ -1349,7 +1339,6 @@ class MaxNLocator(Locator):
     """
     default_params = dict(nbins=10,
                           steps=None,
-                          trim=True,
                           integer=False,
                           symmetric=False,
                           prune=None)
@@ -1385,9 +1374,6 @@ def __init__(self, *args, **kwargs):
             will be removed.  If prune==None, no ticks will be removed.
 
         """
-        # I left "trim" out; it defaults to True, and it is not
-        # clear that there is any use case for False, so we may
-        # want to remove that kwarg.  EF 2010/04/18
         if args:
             kwargs['nbins'] = args[0]
             if len(args) > 1:
@@ -1403,7 +1389,8 @@ def set_params(self, **kwargs):
             if self._nbins != 'auto':
                 self._nbins = int(self._nbins)
         if 'trim' in kwargs:
-            self._trim = kwargs['trim']
+            warnings.warn("The 'trim' keyword has no effect anymore",
+                          mplDeprecation)
         if 'integer' in kwargs:
             self._integer = kwargs['integer']
         if 'symmetric' in kwargs:
@@ -1446,14 +1433,14 @@ def bin_boundaries(self, vmin, vmax):
             if step < scaled_raw_step:
                 continue
             step *= scale
-            best_vmin = step * divmod(vmin, step)[0]
+            best_vmin = vmin // step * step
             best_vmax = best_vmin + step * nbins
-            if (best_vmax >= vmax):
+            if best_vmax >= vmax:
                 break
-        if self._trim:
-            extra_bins = int(divmod((best_vmax - vmax), step)[0])
-            nbins -= extra_bins
-        return (np.arange(nbins + 1) * step + best_vmin + offset)
+
+        bounds = np.arange(nbins + 1) * step + best_vmin
+        bounds = bounds[(bounds >= vmin) & (bounds <= vmax)]
+        return bounds + offset
 
     def __call__(self):
         vmin, vmax = self.axis.get_view_interval()