extend declarative colorbar functionality

src/metpy/plots/declarative.py

@@ -14,8 +14,8 @@
 import matplotlib.pyplot as plt
 import numpy as np
 import pandas as pd
-from traitlets import (Any, Bool, Float, HasTraits, Instance, Int, List, observe, TraitError,
-                       Tuple, Unicode, Union, validate)
+from traitlets import (Any, Bool, Dict, Float, HasTraits, Instance, Int, List, observe,
+                       TraitError, Tuple, Unicode, Union, validate)
 
 from . import ctables, wx_symbols
 from ._mpl import TextCollection
@@ -825,8 +825,12 @@ def draw(self):
             if getattr(self, 'handle', None) is None:
                 self._build()
             if getattr(self, 'colorbar', None) is not None:
-                cbar = self.parent.ax.figure.colorbar(
-                    self.handle, orientation=self.colorbar, pad=0, aspect=50)
+                if isinstance(self.colorbar, dict):
+                    cbar = self.parent.ax.figure.colorbar(
+                        self.handle, **self.colorbar)
+                else:
+                    cbar = self.parent.ax.figure.colorbar(
+                        self.handle, orientation=self.colorbar, pad=0, aspect=50)
                 cbar.ax.tick_params(labelsize=self.colorbar_fontsize)
             self._need_redraw = False
 
@@ -878,13 +882,15 @@ class ColorfillTraits(MetPyHasTraits):
     `matplotlib.colors.Normalize` instance for plotting.
     """
 
-    colorbar = Unicode(default_value=None, allow_none=True)
+    colorbar = Union([Unicode(default_value=None, allow_none=True), Dict()])
     colorbar.__doc__ = """A string (horizontal/vertical) on whether to add a colorbar to the
     plot.
 
-    To add a colorbar associated with the plot, set the trait to ``horizontal`` or
-    ``vertical``,specifying the orientation of the produced colorbar. The default value is
-    ``None``.
+    To add a colorbar associated with the plot, you can either set the trait with a string of
+    ``horizontal`` or ``vertical``, which specifies the orientation of the produced colorbar
+    and uses pre-defined defaults for aspect and pad. Alternatively, you can set a dictionary
+    of keyword argument values valid for a Matplotlib colorbar to specify how the colorbar will
+    be plotted. The default value is ``None``.
     """
 
     colorbar_fontsize = Union([Int(), Float(), Unicode()], allow_none=True, default_value=None)

tests/plots/test_declarative.py

@@ -693,6 +693,31 @@ def test_colorfill_horiz_colorbar(cfeature):
     return pc.figure
 
 
+@pytest.mark.mpl_image_compare(remove_text=True, tolerance=0.02)
+def test_colorbar_kwargs(cfeature):
+    """Test that we can use ContourFillPlot with specifying colorbar kwargs."""
+    data = xr.open_dataset(get_test_data('narr_example.nc', as_file_obj=False))
+
+    contour = FilledContourPlot()
+    contour.data = data
+    contour.level = 700 * units.hPa
+    contour.field = 'Temperature'
+    contour.colormap = 'coolwarm'
+    contour.colorbar = {'orientation': 'horizontal', 'aspect': 60, 'pad': 0.05}
+
+    panel = MapPanel()
+    panel.area = (-110, -60, 25, 55)
+    panel.layers = []
+    panel.plots = [contour]
+
+    pc = PanelContainer()
+    pc.panel = panel
+    pc.size = (8, 8)
+    pc.draw()
+
+    return pc.figure
+
+
 @pytest.mark.mpl_image_compare(remove_text=True, tolerance=0.02)
 def test_colorfill_no_colorbar(cfeature):
     """Test that we can use ContourFillPlot with no colorbar."""