matplotlib broke compatibility with get_cmap in new release (3.9)

[tmroyal]

matplotlib broke compatibility with get_cmap in new release (3.9)

When executing the base example on a newly installed version of py-pde:

import pde

grid = pde.UnitGrid([32,32])
state = pde.ScalarField.random_uniform(grid, -1, 1)

eq = pde.DiffusionPDE(diffusivity=0.1)
result = eq.solve(state, t_range=1, dt=0.01)
result.plot()

I receive the following traceback, which was subsequently solved by performing the command pip install --force-reinstall "matplotlib==3.8.3", which downgrades matplotlib to 3.8.3.

Other packages seem to be having the same issue (atarashansky/SAMap#148).

---------------------------------------------------------------------------
ModuleNotFoundError                       Traceback (most recent call last)
File ~/Documents/composition/opuses2024/coding_projects/pde_play/.venv/lib/python3.11/site-packages/pde/fields/collection.py:21
     [20](https://file+.vscode-resource.vscode-cdn.net/Users/tmroyal/Documents/composition/opuses2024/coding_projects/pde_play/~/Documents/composition/opuses2024/coding_projects/pde_play/.venv/lib/python3.11/site-packages/pde/fields/collection.py:20) try:
---> [21](https://file+.vscode-resource.vscode-cdn.net/Users/tmroyal/Documents/composition/opuses2024/coding_projects/pde_play/~/Documents/composition/opuses2024/coding_projects/pde_play/.venv/lib/python3.11/site-packages/pde/fields/collection.py:21)     from matplotlib.colormaps import get_cmap
     [22](https://file+.vscode-resource.vscode-cdn.net/Users/tmroyal/Documents/composition/opuses2024/coding_projects/pde_play/~/Documents/composition/opuses2024/coding_projects/pde_play/.venv/lib/python3.11/site-packages/pde/fields/collection.py:22) except ImportError:

ModuleNotFoundError: No module named 'matplotlib.colormaps'

During handling of the above exception, another exception occurred:

ImportError                               Traceback (most recent call last)
Cell In[3], [line 1](vscode-notebook-cell:?execution_count=3&line=1)
----> [1](vscode-notebook-cell:?execution_count=3&line=1) import pde
      [3](vscode-notebook-cell:?execution_count=3&line=3) grid = pde.UnitGrid
      [4](vscode-notebook-cell:?execution_count=3&line=4) state = pde.ScalarField.random_uniform(grid)

File ~/Documents/composition/opuses2024/coding_projects/pde_play/.venv/lib/python3.11/site-packages/pde/__init__.py:28
     [25](https://file+.vscode-resource.vscode-cdn.net/Users/tmroyal/Documents/composition/opuses2024/coding_projects/pde_play/~/Documents/composition/opuses2024/coding_projects/pde_play/.venv/lib/python3.11/site-packages/pde/__init__.py:25) del Config  # clean name space
     [27](https://file+.vscode-resource.vscode-cdn.net/Users/tmroyal/Documents/composition/opuses2024/coding_projects/pde_play/~/Documents/composition/opuses2024/coding_projects/pde_play/.venv/lib/python3.11/site-packages/pde/__init__.py:27) # import all other modules that should occupy the main name space
---> [28](https://file+.vscode-resource.vscode-cdn.net/Users/tmroyal/Documents/composition/opuses2024/coding_projects/pde_play/~/Documents/composition/opuses2024/coding_projects/pde_play/.venv/lib/python3.11/site-packages/pde/__init__.py:28) from .fields import *  # @UnusedWildImport
     [29](https://file+.vscode-resource.vscode-cdn.net/Users/tmroyal/Documents/composition/opuses2024/coding_projects/pde_play/~/Documents/composition/opuses2024/coding_projects/pde_play/.venv/lib/python3.11/site-packages/pde/__init__.py:29) from .grids import *  # @UnusedWildImport
     [30](https://file+.vscode-resource.vscode-cdn.net/Users/tmroyal/Documents/composition/opuses2024/coding_projects/pde_play/~/Documents/composition/opuses2024/coding_projects/pde_play/.venv/lib/python3.11/site-packages/pde/__init__.py:30) from .pdes import *  # @UnusedWildImport

File ~/Documents/composition/opuses2024/coding_projects/pde_play/.venv/lib/python3.11/site-packages/pde/fields/__init__.py:26
      [1](https://file+.vscode-resource.vscode-cdn.net/Users/tmroyal/Documents/composition/opuses2024/coding_projects/pde_play/~/Documents/composition/opuses2024/coding_projects/pde_play/.venv/lib/python3.11/site-packages/pde/fields/__init__.py:1) """
      [2](https://file+.vscode-resource.vscode-cdn.net/Users/tmroyal/Documents/composition/opuses2024/coding_projects/pde_play/~/Documents/composition/opuses2024/coding_projects/pde_play/.venv/lib/python3.11/site-packages/pde/fields/__init__.py:2) Defines fields, which contain the actual data stored on a discrete grid.
      [3](https://file+.vscode-resource.vscode-cdn.net/Users/tmroyal/Documents/composition/opuses2024/coding_projects/pde_play/~/Documents/composition/opuses2024/coding_projects/pde_play/.venv/lib/python3.11/site-packages/pde/fields/__init__.py:3) 
   (...)
     [22](https://file+.vscode-resource.vscode-cdn.net/Users/tmroyal/Documents/composition/opuses2024/coding_projects/pde_play/~/Documents/composition/opuses2024/coding_projects/pde_play/.venv/lib/python3.11/site-packages/pde/fields/__init__.py:22) .. codeauthor:: David Zwicker <[email protected]>
     [23](https://file+.vscode-resource.vscode-cdn.net/Users/tmroyal/Documents/composition/opuses2024/coding_projects/pde_play/~/Documents/composition/opuses2024/coding_projects/pde_play/.venv/lib/python3.11/site-packages/pde/fields/__init__.py:23) """
     [25](https://file+.vscode-resource.vscode-cdn.net/Users/tmroyal/Documents/composition/opuses2024/coding_projects/pde_play/~/Documents/composition/opuses2024/coding_projects/pde_play/.venv/lib/python3.11/site-packages/pde/fields/__init__.py:25) from .base import FieldBase
---> [26](https://file+.vscode-resource.vscode-cdn.net/Users/tmroyal/Documents/composition/opuses2024/coding_projects/pde_play/~/Documents/composition/opuses2024/coding_projects/pde_play/.venv/lib/python3.11/site-packages/pde/fields/__init__.py:26) from .collection import FieldCollection
     [27](https://file+.vscode-resource.vscode-cdn.net/Users/tmroyal/Documents/composition/opuses2024/coding_projects/pde_play/~/Documents/composition/opuses2024/coding_projects/pde_play/.venv/lib/python3.11/site-packages/pde/fields/__init__.py:27) from .scalar import ScalarField
     [28](https://file+.vscode-resource.vscode-cdn.net/Users/tmroyal/Documents/composition/opuses2024/coding_projects/pde_play/~/Documents/composition/opuses2024/coding_projects/pde_play/.venv/lib/python3.11/site-packages/pde/fields/__init__.py:28) from .tensorial import Tensor2Field

File ~/Documents/composition/opuses2024/coding_projects/pde_play/.venv/lib/python3.11/site-packages/pde/fields/collection.py:23
     [21](https://file+.vscode-resource.vscode-cdn.net/Users/tmroyal/Documents/composition/opuses2024/coding_projects/pde_play/~/Documents/composition/opuses2024/coding_projects/pde_play/.venv/lib/python3.11/site-packages/pde/fields/collection.py:21)     from matplotlib.colormaps import get_cmap
     [22](https://file+.vscode-resource.vscode-cdn.net/Users/tmroyal/Documents/composition/opuses2024/coding_projects/pde_play/~/Documents/composition/opuses2024/coding_projects/pde_play/.venv/lib/python3.11/site-packages/pde/fields/collection.py:22) except ImportError:
---> [23](https://file+.vscode-resource.vscode-cdn.net/Users/tmroyal/Documents/composition/opuses2024/coding_projects/pde_play/~/Documents/composition/opuses2024/coding_projects/pde_play/.venv/lib/python3.11/site-packages/pde/fields/collection.py:23)     from matplotlib.cm import get_cmap
     [25](https://file+.vscode-resource.vscode-cdn.net/Users/tmroyal/Documents/composition/opuses2024/coding_projects/pde_play/~/Documents/composition/opuses2024/coding_projects/pde_play/.venv/lib/python3.11/site-packages/pde/fields/collection.py:25) from ..grids.base import GridBase
     [26](https://file+.vscode-resource.vscode-cdn.net/Users/tmroyal/Documents/composition/opuses2024/coding_projects/pde_play/~/Documents/composition/opuses2024/coding_projects/pde_play/.venv/lib/python3.11/site-packages/pde/fields/collection.py:26) from ..tools.docstrings import fill_in_docstring

ImportError: cannot import name 'get_cmap' from 'matplotlib.cm' (/Users/tmroyal/Documents/composition/opuses2024/coding_projects/pde_play/.venv/lib/python3.11/site-packages/matplotlib/cm.py)