FIX: add support for imshow extent to have units

Author: pratimugale

doc/users/next_whats_new/imshow_extent_units.rst

@@ -0,0 +1,26 @@
+The *extent* of ``imshow`` can now be expressed with units
+----------------------------------------------------------
+The *extent* parameter of `~.axes.Axes.imshow` and  `~.AxesImage.set_extent`
+can now be expressed with units.
+
+.. plot::
+    :include-source: true
+
+    import matplotlib.pyplot as plt
+    import numpy as np
+    from matplotlib.dates import HourLocator, DateFormatter
+    from matplotlib.ticker import AutoMinorLocator
+
+    fig, ax = plt.subplots()
+    date_first = np.datetime64('2020-01-01', 'D')
+    date_last = np.datetime64('2020-01-11', 'D')
+
+    arr = [[i+j for i in range(10)] for j in range(10)]
+
+    ax.imshow(arr, origin='lower', extent=[1, 11, date_first, date_last])
+
+    ax.yaxis.set_major_formatter(DateFormatter('%d/%m/%y:- %H00hours'))
+    ax.yaxis.set_major_locator(HourLocator(byhour=[0, 6, 12, 18, 24]))
+    ax.yaxis.set_minor_locator(AutoMinorLocator())
+
+    plt.show()

lib/matplotlib/axes/_axes.py

@@ -5555,6 +5555,7 @@ def imshow(self, X, cmap=None, norm=None, aspect=None,
 
         extent : floats (left, right, bottom, top), optional
             The bounding box in data coordinates that the image will fill.
+            These values may be unitful and match the units of the Axes.
             The image is stretched individually along x and y to fill the box.
 
             The default extent is determined by the following conditions.

lib/matplotlib/image.py

@@ -953,7 +953,7 @@ def _check_unsampled_image(self):
         """Return whether the image would be better drawn unsampled."""
         return self.get_interpolation() == "none"
 
-    def set_extent(self, extent):
+    def set_extent(self, extent, **kwargs):
         """
         Set the image extent.
 
@@ -962,6 +962,10 @@ def set_extent(self, extent):
         extent : 4-tuple of float
             The position and size of the image as tuple
             ``(left, right, bottom, top)`` in data coordinates.
+        **kwargs
+            Other parameters from which unit info (i.e., the *xunits*,
+            *yunits*, *zunits* (for 3D axes), *runits* and *thetaunits* (for
+            polar axes) entries are applied, if present.
 
         Notes
         -----
@@ -970,7 +974,26 @@ def set_extent(self, extent):
         state is not changed, so following this with ``ax.autoscale_view()``
         will redo the autoscaling in accord with ``dataLim``.
         """
-        self._extent = xmin, xmax, ymin, ymax = extent
+        (xmin, xmax), (ymin, ymax) = self.axes._process_unit_info(
+            [("x", [extent[0], extent[1]]),
+             ("y", [extent[2], extent[3]])],
+            kwargs)
+        if len(kwargs):
+            raise ValueError(
+                "set_extent did not consume all of the kwargs passed." +
+                f"{list(kwargs)!r} were unused"
+            )
+        xmin = self.axes._validate_converted_limits(
+            xmin, self.convert_xunits)
+        xmax = self.axes._validate_converted_limits(
+            xmax, self.convert_xunits)
+        ymin = self.axes._validate_converted_limits(
+            ymin, self.convert_yunits)
+        ymax = self.axes._validate_converted_limits(
+            ymax, self.convert_yunits)
+        extent = [xmin, xmax, ymin, ymax]
+
+        self._extent = extent
         corners = (xmin, ymin), (xmax, ymax)
         self.axes.update_datalim(corners)
         self.sticky_edges.x[:] = [xmin, xmax]

lib/matplotlib/tests/baseline_images/test_axes/extent_units.png

@@ -8272,3 +8272,39 @@ def test_bar_all_nan(fig_test, fig_ref):
 
     ax_ref.bar([1], [1]).remove()
     ax_ref.bar([1], [1])
+
+
+@image_comparison(["extent_units.png"], style="mpl20")
+def test_extent_units():
+    _, axs = plt.subplots(2, 2)
+    date_first = np.datetime64('2020-01-01', 'D')
+    date_last = np.datetime64('2020-01-11', 'D')
+    arr = [[i+j for i in range(10)] for j in range(10)]
+
+    axs[0, 0].set_title('Date extents on y axis')
+    im = axs[0, 0].imshow(arr, origin='lower',
+                          extent=[1, 11, date_first, date_last],
+                          cmap=mpl.colormaps["plasma"])
+
+    axs[0, 1].set_title('Date extents on x axis (Day of Jan 2020)')
+    im = axs[0, 1].imshow(arr, origin='lower',
+                          extent=[date_first, date_last, 1, 11],
+                          cmap=mpl.colormaps["plasma"])
+    axs[0, 1].xaxis.set_major_formatter(mdates.DateFormatter('%d'))
+
+    im = axs[1, 0].imshow(arr, origin='lower',
+                          extent=[date_first, date_last,
+                                  date_first, date_last],
+                          cmap=mpl.colormaps["plasma"])
+    axs[1, 0].xaxis.set_major_formatter(mdates.DateFormatter('%d'))
+    axs[1, 0].set(xlabel='Day of Jan 2020')
+
+    im = axs[1, 1].imshow(arr, origin='lower',
+                          cmap=mpl.colormaps["plasma"])
+    im.set_extent([date_last, date_first, date_last, date_first])
+    axs[1, 1].xaxis.set_major_formatter(mdates.DateFormatter('%d'))
+    axs[1, 1].set(xlabel='Day of Jan 2020')
+
+    with pytest.raises(ValueError,
+                       match="set_extent did not consume all of the kwargs"):
+        im.set_extent([2, 12, date_first, date_last], clip=False)