Let Formatters format all ticks at once.

anntzer · anntzer · commit b715a349a448 · 2019-01-28T22:33:38.000+01:00
This is useful especially when labels are interdependent (e.g.
ConciseDateFormatter, but also LogFormatter which currently relies on
set_locs, etc.).

Because `set_major_formatter`/`set_minor_formatter` (somewhat unusually)
enforces that its argument is a Formatter subclass, even third-party
formatters will inherit from the base class and have this method
defined.
diff --git a/doc/api/next_api_changes/2018-01-28-AL.rst b/doc/api/next_api_changes/2018-01-28-AL.rst
@@ -0,0 +1,11 @@
+New `Formatter.format_ticks` method
+```````````````````````````````````
+
+The `Formatter` class gained a new `~Formatter.format_ticks` methods, which
+takes the list of all tick locations as single argument and returns the list
+of all formatted values.  It is called by the axis tick handling code and, by
+default, repeatedly calls `~Formatter.__call__`.
+
+It is intended to be overridden by `Formatter` subclasses for which
+the formatting of a tick value depends on other tick values, such as
+`ConciseDateFormatter`.
diff --git a/lib/matplotlib/axis.py b/lib/matplotlib/axis.py
@@ -929,24 +929,18 @@ def iter_ticks(self):
         """
         Iterate through all of the major and minor ticks.
         """
-        majorLocs = self.major.locator()
-        majorTicks = self.get_major_ticks(len(majorLocs))
-        self.major.formatter.set_locs(majorLocs)
-        majorLabels = [self.major.formatter(val, i)
-                       for i, val in enumerate(majorLocs)]
-
-        minorLocs = self.minor.locator()
-        minorTicks = self.get_minor_ticks(len(minorLocs))
-        self.minor.formatter.set_locs(minorLocs)
-        minorLabels = [self.minor.formatter(val, i)
-                       for i, val in enumerate(minorLocs)]
-
-        major_minor = [
-            (majorTicks, majorLocs, majorLabels),
-            (minorTicks, minorLocs, minorLabels)]
-
-        for group in major_minor:
-            yield from zip(*group)
+        major_locs = self.major.locator()
+        major_ticks = self.get_major_ticks(len(major_locs))
+        self.major.formatter.set_locs(major_locs)
+        major_labels = self.major.formatter.format_ticks(major_locs)
+
+        minor_locs = self.minor.locator()
+        minor_ticks = self.get_minor_ticks(len(minor_locs))
+        self.minor.formatter.set_locs(minor_locs)
+        minor_labels = self.minor.formatter.format_ticks(minor_locs)
+
+        yield from zip(major_ticks, major_locs, major_labels)
+        yield from zip(minor_ticks, minor_locs, minor_labels)
 
     def get_ticklabel_extents(self, renderer):
         """
diff --git a/lib/matplotlib/colorbar.py b/lib/matplotlib/colorbar.py
@@ -789,7 +789,7 @@ def _ticker(self, locator, formatter):
         self._manual_tick_data_values = b
         ticks = self._locate(b)
         formatter.set_locs(b)
-        ticklabels = [formatter(t, i) for i, t in enumerate(b)]
+        ticklabels = formatter.format_ticks(b)
         offset_string = formatter.get_offset()
         return ticks, ticklabels, offset_string
 
diff --git a/lib/matplotlib/ticker.py b/lib/matplotlib/ticker.py
@@ -253,6 +253,10 @@ def __call__(self, x, pos=None):
         """
         raise NotImplementedError('Derived must override')
 
+    def format_ticks(self, values):
+        """Return the tick labels for all the ticks at once."""
+        return [self(value, i) for i, value in enumerate(values)]
+
     def format_data(self, value):
         """
         Returns the full string representation of the value with the
@@ -291,7 +295,7 @@ def fix_minus(self, s):
         return s
 
     def _set_locator(self, locator):
-        """ Subclasses may want to override this to set a locator. """
+        """Subclasses may want to override this to set a locator."""
         pass
 
 
diff --git a/lib/mpl_toolkits/axisartist/axislines.py b/lib/mpl_toolkits/axisartist/axislines.py
@@ -226,14 +226,12 @@ def get_tick_iterators(self, axes):
             major = self.axis.major
             majorLocs = major.locator()
             major.formatter.set_locs(majorLocs)
-            majorLabels = [major.formatter(val, i)
-                           for i, val in enumerate(majorLocs)]
+            majorLabels = major.formatter.format_ticks(majorLocs)
 
             minor = self.axis.minor
             minorLocs = minor.locator()
             minor.formatter.set_locs(minorLocs)
-            minorLabels = [minor.formatter(val, i)
-                           for i, val in enumerate(minorLocs)]
+            minorLabels = minor.formatter.format_ticks(minorLocs)
 
             trans_tick = self.get_tick_transform(axes)
 
@@ -323,14 +321,12 @@ def get_tick_iterators(self, axes):
             major = self.axis.major
             majorLocs = major.locator()
             major.formatter.set_locs(majorLocs)
-            majorLabels = [major.formatter(val, i)
-                           for i, val in enumerate(majorLocs)]
+            majorLabels = major.formatter.format_ticks(majorLocs)
 
             minor = self.axis.minor
             minorLocs = minor.locator()
             minor.formatter.set_locs(minorLocs)
-            minorLabels = [minor.formatter(val, i)
-                           for i, val in enumerate(minorLocs)]
+            minorLabels = minor.formatter.format_ticks(minorLocs)
 
             tr2ax = axes.transData + axes.transAxes.inverted()
 
