matplotlib · jklymak · Feb 7, 2019 · Jan 13, 2019
diff --git a/doc/api/next_api_changes/2018-01-10-AL.rst b/doc/api/next_api_changes/2018-01-10-AL.rst
@@ -16,6 +16,11 @@ In each case, the old parameter name remains supported (it cannot be used
 simultaneously with the new name), but suppport for it will be dropped in
 Matplotlib 3.3.
 
+- The unused ``shape`` and ``imlim`` parameters to `Axes.imshow` are
+  deprecated.  To avoid triggering the deprecation warning, the ``filternorm``,
+  ``filterrad``, ``resample``, and ``url`` arguments should be passed by
+  keyword.
+
 Deprecations
 ````````````
 

diff --git a/lib/matplotlib/axes/_axes.py b/lib/matplotlib/axes/_axes.py
@@ -5395,6 +5395,8 @@ def get_interp_point(ind):
 
     #### plotting z(x,y): imshow, pcolor and relatives, contour
     @_preprocess_data()
+    @cbook._delete_parameter("3.1", "shape")
+    @cbook._delete_parameter("3.1", "imlim")
     def imshow(self, X, cmap=None, norm=None, aspect=None,
                interpolation=None, alpha=None, vmin=None, vmax=None,
                origin=None, extent=None, shape=None, filternorm=1,
@@ -5508,9 +5510,6 @@ def imshow(self, X, cmap=None, norm=None, aspect=None,
             See the example :doc:`/tutorials/intermediate/imshow_extent` for a
             more detailed description.
 
-        shape : scalars (columns, rows), optional, default: None
-            For raw buffer images.
-
         filternorm : bool, optional, default: True
             A parameter for the antigrain image resize filter (see the
             antigrain documentation).  If *filternorm* is set, the filter

diff --git a/lib/matplotlib/cbook/__init__.py b/lib/matplotlib/cbook/__init__.py
@@ -32,7 +32,7 @@
 
 import matplotlib
 from .deprecation import (
-    deprecated, warn_deprecated, _rename_parameter,
+    deprecated, warn_deprecated, _rename_parameter, _delete_parameter,
     _suppress_matplotlib_deprecation_warning,
     MatplotlibDeprecationWarning, mplDeprecation)
 

diff --git a/lib/matplotlib/cbook/deprecation.py b/lib/matplotlib/cbook/deprecation.py
@@ -310,6 +310,63 @@ def wrapper(*args, **kwargs):
     return wrapper
 
 
+class _deprecated_parameter_class:
+    def __repr__(self):
+        return "<deprecated parameter>"
+
+
+_deprecated_parameter = _deprecated_parameter_class()
+
+
+def _delete_parameter(since, name, func=None):
+    """
+    Decorator indicating that parameter *name* of *func* is being deprecated.
+
+    The actual implementation of *func* should keep the *name* parameter in its
+    signature.
+
+    Parameters that come after the deprecated parameter effectively become
+    keyword-only (as they cannot be passed positionally without triggering the
+    DeprecationWarning on the deprecated parameter), and should be marked as
+    such after the deprecation period has passed and the deprecated parameter
+    is removed.
+
+    Examples
+    --------
+
+    ::
+        @_delete_parameter("3.1", "unused")
+        def func(used_arg, other_arg, unused, more_args): ...
+    """
+
+    if func is None:
+        return functools.partial(_delete_parameter, since, name)
+
+    signature = inspect.signature(func)
+    assert name in signature.parameters, (
+        f"Matplotlib internal error: {name!r} must be a parameter for "
+        f"{func.__name__}()")
+    func.__signature__ = signature.replace(parameters=[
+        param.replace(default=_deprecated_parameter) if param.name == name
+        else param
+        for param in signature.parameters.values()])
+
+    @functools.wraps(func)
+    def wrapper(*args, **kwargs):
+        arguments = func.__signature__.bind(*args, **kwargs).arguments
+        # We cannot just check `name not in arguments` because the pyplot
+        # wrappers always pass all arguments explicitly.
+        if name in arguments and arguments[name] != _deprecated_parameter:
+            warn_deprecated(
+                since, message=f"The {name!r} parameter of {func.__name__}() "
+                f"is deprecated since Matplotlib {since} and will be removed "
+                f"%(removal)s.  If any parameter follows {name!r}, they "
+                f"should be pass as keyword, not positionally.")
+        return func(*args, **kwargs)
+
+    return wrapper
+
+
 @contextlib.contextmanager
 def _suppress_matplotlib_deprecation_warning():
     with warnings.catch_warnings():

diff --git a/lib/matplotlib/pyplot.py b/lib/matplotlib/pyplot.py
@@ -2644,7 +2644,8 @@ def hlines(
 def imshow(
         X, cmap=None, norm=None, aspect=None, interpolation=None,
         alpha=None, vmin=None, vmax=None, origin=None, extent=None,
-        shape=None, filternorm=1, filterrad=4.0, imlim=None,
+        shape=cbook.deprecation._deprecated_parameter, filternorm=1,
+        filterrad=4.0, imlim=cbook.deprecation._deprecated_parameter,
         resample=None, url=None, *, data=None, **kwargs):
     __ret = gca().imshow(
         X, cmap=cmap, norm=norm, aspect=aspect,

diff --git a/lib/matplotlib/tests/test_image.py b/lib/matplotlib/tests/test_image.py
@@ -15,6 +15,7 @@
 from matplotlib import (
     colors, image as mimage, patches, pyplot as plt,
     rc_context, rcParams)
+from matplotlib.cbook import MatplotlibDeprecationWarning
 from matplotlib.image import (AxesImage, BboxImage, FigureImage,
                               NonUniformImage, PcolorImage)
 from matplotlib.testing.decorators import image_comparison
@@ -944,3 +945,17 @@ def test_relim():
     ax.relim()
     ax.autoscale()
     assert ax.get_xlim() == ax.get_ylim() == (0, 1)
+
+
+def test_deprecation():
+    data = [[1, 2], [3, 4]]
+    ax = plt.figure().subplots()
+    for obj in [ax, plt]:
+        with pytest.warns(None) as record:
+            obj.imshow(data)
+            assert len(record) == 0
+        with pytest.warns(MatplotlibDeprecationWarning):
+            obj.imshow(data, shape=None)
+        with pytest.warns(MatplotlibDeprecationWarning):
+            # Enough arguments to pass "shape" positionally.
+            obj.imshow(data, *[None] * 10)
diff --git a/tools/boilerplate.py b/tools/boilerplate.py
@@ -20,7 +20,7 @@
 
 # This line imports the installed copy of matplotlib, and not the local copy.
 import numpy as np
-from matplotlib import mlab
+from matplotlib import cbook, mlab
 from matplotlib.axes import Axes
 
 
@@ -175,6 +175,8 @@ def __init__(self, value):
                 self._repr = "mlab.window_hanning"
             elif value is np.mean:
                 self._repr = "np.mean"
+            elif value is cbook.deprecation._deprecated_parameter:
+                self._repr = "cbook.deprecation._deprecated_parameter"
             else:
                 self._repr = repr(value)