better perfs

yt/visualization/plot_container.py

@@ -1,8 +1,9 @@
 import base64
 import builtins
 import os
+import sys
 import textwrap
-from collections import ChainMap, defaultdict
+from collections import defaultdict
 from functools import wraps
 
 import matplotlib
@@ -271,9 +272,12 @@ def __init__(self, data_source, figure_size, fontsize):
         else:
             self.figure_size = float(figure_size)
 
-        font_props = _DEFAULT_FONT_PROPERTIES.copy()
-        font_props["size"] = fontsize
-        self._font_properties = FontProperties(**font_props)
+        if sys.version_info >= (3, 9):
+            font_dict = _DEFAULT_FONT_PROPERTIES | {"size": fontsize}
+        else:
+            font_dict = {**_DEFAULT_FONT_PROPERTIES, "size": fontsize}
+
+        self._font_properties = FontProperties(**font_dict)
         self._font_color = None
         self._xlabel = None
         self._ylabel = None
@@ -528,8 +532,11 @@ def set_font(self, font_dict=None):
             self._font_color = font_dict.pop("color")
         # Set default values if the user does not explicitly set them.
         # this prevents reverting to the matplotlib defaults.
-        font_props = ChainMap(font_dict, _DEFAULT_FONT_PROPERTIES)
-        self._font_properties = FontProperties(**font_props)
+        if sys.version_info >= (3, 9):
+            font_dict = _DEFAULT_FONT_PROPERTIES | font_dict
+        else:
+            font_dict = {**_DEFAULT_FONT_PROPERTIES, **font_dict}
+        self._font_properties = FontProperties(**font_dict)
         return self
 
     def set_font_size(self, size):