Don't trigger matplotlib.__getattr__("__version__") if possible.

lib/mplcairo/__init__.py

@@ -1,8 +1,10 @@
 import ast
+import functools
 import os
 import sys
 import warnings
 
+
 try:
     from ._version import version as __version__
 except ImportError:
@@ -54,18 +56,32 @@ def _init_options():
 _init_options()
 
 
+@functools.lru_cache(1)
+def _get_mpl_version():
+    # Don't trigger a git subprocess for Matplotlib's __version__ resolution if
+    # possible, and cache the result as early versions of importlib.metadata
+    # are slow.  We can't cache get_versions() directly as the result depends
+    # on whether raqm is loaded.
+    try:
+        import importlib.metadata
+        return importlib.metadata.version("matplotlib")
+    except ImportError:
+        # No importlib.metadata on Py<3.8 *or* not-installed Matplotlib.
+        return matplotlib.__version__
+
+
 def get_versions():
     """
     Return a mapping indicating the versions of mplcairo and its dependencies.
 
-    This function is solely intended to help gather information for bug
-    reports; its output may change without notice.
+    This function is intended to help gather information for bug reports, and
+    not part of the stable API.
     """
     versions = _mplcairo.get_versions()
     return {
         "python": sys.version,
         "mplcairo": __version__,
-        "matplotlib": matplotlib.__version__,
+        "matplotlib": _get_mpl_version(),
         **versions,
     }
 

lib/mplcairo/base.py

@@ -22,7 +22,7 @@
 from matplotlib.backends import backend_ps
 from matplotlib.mathtext import MathTextParser
 
-from . import _mplcairo, _util
+from . import _mplcairo, _util, get_versions
 from ._backports import get_glyph_name
 from ._mplcairo import _StreamSurfaceType
 
@@ -404,7 +404,8 @@ def print_png(self, path_or_stream, *,
             return
         metadata = {
             "Software":
-            f"matplotlib version {mpl.__version__}, https://matplotlib.org",
+            f"matplotlib version {get_versions()['matplotlib']}, "
+            f"https://matplotlib.org",
             **(metadata if metadata is not None else {}),
         }
         if pil_kwargs is None: