perf(plotting): improve module import time

Accelerates initial import time by refactoring heavy imports to reside inside functions. Furthermore, automatically importing cmocean, cmasher, and colorcet packages are now disabled. The user must import them manually to access those colormaps.

src/erlab/plotting/__init__.py

@@ -19,7 +19,6 @@
 
 """
 
-import importlib
 import io
 import os
 import pkgutil
@@ -30,14 +29,6 @@
 import matplotlib.style
 import numpy as np
 
-# Import colormaps if available
-if importlib.util.find_spec("cmasher"):
-    importlib.import_module("cmasher")
-if importlib.util.find_spec("cmocean"):
-    importlib.import_module("cmocean")
-if importlib.util.find_spec("colorcet"):
-    importlib.import_module("colorcet")
-
 
 def load_igor_ct(
     file: str | os.PathLike | io.BytesIO, name: str, register_reversed: bool = True

src/erlab/plotting/annotations.py

@@ -28,8 +28,6 @@
 from typing import TYPE_CHECKING, Any, Literal, cast
 
 import matplotlib
-import matplotlib.backends.backend_pdf
-import matplotlib.backends.backend_svg
 import matplotlib.figure
 import matplotlib.font_manager
 import matplotlib.mathtext
@@ -286,8 +284,12 @@ def copy_mathtext(
     fig.text(0, depth / height, s, fontproperties=fontproperties)
 
     if svg:
+        import matplotlib.backends.backend_svg
+
         matplotlib.backends.backend_svg.FigureCanvasSVG(fig)
     else:
+        import matplotlib.backends.backend_pdf
+
         matplotlib.backends.backend_pdf.FigureCanvasPdf(fig)
 
     for k, v in mathtext_rc.items():

src/erlab/plotting/bz.py

@@ -8,7 +8,6 @@
 import matplotlib.pyplot as plt
 import numpy as np
 import numpy.typing as npt
-import scipy.spatial
 from matplotlib.patches import RegularPolygon
 
 from erlab.plotting.colors import axes_textcolor
@@ -70,6 +69,8 @@ def get_bz_edge(
     # Get index of origin
     zero_ind = np.where((points == 0).all(axis=1))[0][0]
 
+    import scipy.spatial
+
     vor = scipy.spatial.Voronoi(points)
 
     lines = []

src/erlab/plotting/colors.py

@@ -7,8 +7,7 @@
 <https://matplotlib.org/stable/tutorials/colors/colormaps.html>`_ colormaps, `cmasher
 <https://cmasher.readthedocs.io>`_, `cmocean <https://matplotlib.org/cmocean/>`_, and
 `colorcet <https://colorcet.holoviz.org>`_ packages can be installed to extend the
-available colormaps. If these packages are installed, they will be automatically
-imported upon importing `erlab.plotting`.
+available colormaps.
 
 Colormap Normalization
 ----------------------