Passing clim as keyword argument to pcolormesh does not change limits.

Bug report

Bug summary

Not sure if this is really a bug or just a user issue. I expected that passing a clim tuple to pcolormesh with no vmin or vmax specified would update the color scale limits. I found that I had to use vmin and vmax instead. Maybe I am misunderstanding and vmin and vmax should always be used. However, it looks like the kwargs are passed into the QuadMesh constructor and then clim is overwritten with vmin and vmax, even in they are None and clim is given. (https://github.com/heath730/matplotlib/blob/master/lib/matplotlib/axes/_axes.py#L5629).

Code for reproduction

import matplotlib.pyplot as plt
import numpy as np


plot_me = np.random.rand(5, 5)

plt.subplot(211)
plt.title("Expected")
plt.pcolormesh(plot_me, vmin=0, vmax=0.5)
plt.colorbar()

plt.subplot(212)
plt.title("Result")
plt.pcolormesh(plot_me, clim=(0, 0.5))
plt.colorbar()

plt.show()

Matplotlib version

Operating system: win7
Matplotlib version: 2.1.2
Matplotlib backend (print(matplotlib.get_backend())): TkAgg
Python version: 3.5.1
Jupyter version (if applicable):
Other libraries:

Would something like:

  (vmin, vmax) = kwargs.pop('clim', (None, None))

Before the vmin and vmax pops on this line be a reasonable update?

Do the docs say that you can pass clim? I couldn't find anywhere that they say you can. There is a pyplot.clim but thats a matlab-ism...

I think having a clim argument and vmin/vmax is asking for trouble...

@jklymak

@jklymak They don't list clim as an arg for pcolormesh, but they say the properties of the QuadMesh object that pcolormesh creates can be controlled using kwargs (including clim). However, if you do pass clim it will get overwritten with vmin/vmax. I guess just using vmin/vmax is probably the simplest way to go though, I did come from a matlab background originally so I guess that's why I was trying to use clim instead of vmin/vmax in the first place.

The docs I'm referring to are: https://matplotlib.org/api/_as_gen/matplotlib.axes.Axes.pcolormesh.html

Yep you are right. Thats actually pretty annoying. Not sure what should change. It should be possible to not override clim if vmin and vmax are not provided. But ideally both forms would not exist. I'm not sure what the history is here.

This is long-ago cleverness coming back to bite us. The clim kwarg is being inherited based on the ScalarMappable.set_clim method, via the call to Artist.update in the Collection.__init__. That's why we have all these horrendous tables clogging the documentation: mostly irrelevant "properties", also advertised as "kwargs" and inherited via this circuitous process.

Do you think a note in the docstring that the clim property of the returned QuadMesh will be replaced by vmin/vmax would be appropriate or is it better to leave as is? If I understand your explanation correctly, pcolormesh is not really meant to support clim, but that table is being pulled into the docs because of the class hierarchy.

The docstring is autogenerated from pieces pulled from various places, and used in many places. Maybe it would make sense to add a note to the set_clim docstring to the effect that it should not be used when vmin, vmax are available.

I suspect this clash between clim and vmin, vmax is widespread, and there are probably many other such inherited properties that it would be better not to expose as kwargs. I haven't thought it through, though.

fwiw I would just pass everything to QuadMesh and teach ScalarMappable how to handle them.

diff --git a/lib/matplotlib/axes/_axes.py b/lib/matplotlib/axes/_axes.py
index df2ccd55e..77b9a8089 100644
--- a/lib/matplotlib/axes/_axes.py
+++ b/lib/matplotlib/axes/_axes.py
@@ -5866,11 +5866,6 @@ linewidth=2, markersize=12)
         if not self._hold:
             self.cla()
 
-        alpha = kwargs.pop('alpha', None)
-        norm = kwargs.pop('norm', None)
-        cmap = kwargs.pop('cmap', None)
-        vmin = kwargs.pop('vmin', None)
-        vmax = kwargs.pop('vmax', None)
         shading = kwargs.pop('shading', 'flat').lower()
         antialiased = kwargs.pop('antialiased', False)
         kwargs.setdefault('edgecolors', 'None')
@@ -5892,14 +5887,7 @@ linewidth=2, markersize=12)
         collection = mcoll.QuadMesh(Nx - 1, Ny - 1, coords,
                                     antialiased=antialiased, shading=shading,
                                     **kwargs)
-        collection.set_alpha(alpha)
         collection.set_array(C)
-        if norm is not None and not isinstance(norm, mcolors.Normalize):
-            raise ValueError(
-                "'norm' must be an instance of 'mcolors.Normalize'")
-        collection.set_cmap(cmap)
-        collection.set_norm(norm)
-        collection.set_clim(vmin, vmax)
         collection.autoscale_None()
 
         self.grid(False)
diff --git a/lib/matplotlib/cm.py b/lib/matplotlib/cm.py
index ecd1179f1..c6cc87472 100644
--- a/lib/matplotlib/cm.py
+++ b/lib/matplotlib/cm.py
@@ -318,6 +318,12 @@ class ScalarMappable(object):
             self.norm.vmax = vmax
         self.changed()
 
+    def set_vmin(self, vmin):
+        self.set_clim(vmin=vmin)
+
+    def set_vmax(self, vmax):
+        self.set_clim(vmax=vmax)
+
     def set_cmap(self, cmap):
         """
         set the colormap for luminance data

or, if we decide that's not the route we want to take, we should just deprecate clim, instead of keeping it half-assed...

Note that the above solution will apply kwargs in the order they are given, so 1) that only works on Py3.6+ which keeps kwargs order (by mpl3 is coming :)) and 2) requires the user to pass the norm before the clims, which does not seem unreasonable...

We also have a precedent of just forcing the order of the kwargs to something logically consistent in https://github.com/matplotlib/matplotlib/blob/master/lib/matplotlib/text.py#L178.

You can do that. But you need to decide what takes precedence - vmin/vmax or clim. That’s pretty bad API if there are two ways to do the same thing with arbitrary precedence. I’d prefer to deprecate clim.

Reopening because the documentation change is fine but not really the root of the problem.

I think this was effectively fixed by #21146. Feel free to reopen if not.

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Passing clim as keyword argument to pcolormesh does not change limits. #10346

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Passing clim as keyword argument to pcolormesh does not change limits. #10346

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jklymak commented on Jan 30, 2018

heathhenley commented on Jan 31, 2018

jklymak commented on Jan 31, 2018

efiring commented on Jan 31, 2018

heathhenley commented on Jan 31, 2018

efiring commented on Jan 31, 2018

anntzer commented on Jan 31, 2018

jklymak commented on Jan 31, 2018

anntzer commented on Nov 2, 2021

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