Potential compatibility issues with matplotlib.cm.get_cmap (Incompatible with Matplotlib 3.9.0)

[xyf5432]

Context

We are currently analyzing historical GitHub issues to identify potential compatibility regressions in open-source projects. During this process, we noticed a usage pattern in OpenSfM that corresponds to a known unstable API in matplotlib (matplotlib.cm.get_cmap).

Findings

The deprecated cm.get_cmap API is used in the following files:

• bin/import_colmap.py
• bin/plot_matches.py

Evidence & History

This API has a history of instability. It was briefly removed in Matplotlib in 3.9.0, before being restored in patch releases ( 3.9.1) due to community feedback.

The rationale and future removal plan are explicitly documented in the Matplotlib 3.10.0 source code(https://github.com/matplotlib/matplotlib/blob/v3.10.0/lib/matplotlib/cm.py#L246-255):

# This is an exact copy of pyplot.get_cmap(). It was removed in 3.9, but apparently
# caused more user trouble than expected. Re-added for 3.9.1 and extended the
# deprecation period for two additional minor releases.
@_api.deprecated(
    '3.7',
    removal='3.11',
    alternative="``matplotlib.colormaps[name]`` or ``matplotlib.colormaps.get_cmap()``"
                " or ``pyplot.get_cmap()``"
)
def get_cmap(name=None, lut=None):
    # ...

Potential Impact

1. Suspected Crashes: Users whose environments happen to have 3.9.0 installed likely face immediate AttributeError crashes when running these scripts.
2. Future Incompatibility: As noted in the source code above, the API is scheduled for permanent removal in version 3.11.

Experimental Evidence

Our local testing confirms that matplotlib.cm.get_cmap was physically removed in Matplotlib 3.9.0, leading to an immediate crash.

Verification on Matplotlib 3.9.0:

>>> import matplotlib
>>> print(matplotlib.__version__)
3.9.0
>>> from matplotlib import cm
>>> cmap = cm.get_cmap(None)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: module 'matplotlib.cm' has no attribute 'get_cmap'

Suggestions

Option 1: Update API (Recommended)
Consider updating the code to use the alternatives suggested in the Matplotlib source code (e.g., matplotlib.colormaps[name] or pyplot.get_cmap()) to ensure long-term stability.

Option 2: Restrict Dependency Version
If a code update is not immediate, you might consider temporarily restricting the dependency versions in pyproject.toml to avoid the unstable releases:

dependencies = [
    "matplotlib!=3.9.0,<3.11",
]