Allow default ImageDraw font to be set

Tests/test_imagedraw.py

@@ -1314,6 +1314,23 @@ def test_stroke_multiline():
     assert_image_similar_tofile(im, "Tests/images/imagedraw_stroke_multiline.png", 3.3)
 
 
+def test_setting_default_font():
+    # Arrange
+    im = Image.new("RGB", (100, 250))
+    draw = ImageDraw.Draw(im)
+    font = ImageFont.truetype("Tests/fonts/FreeMono.ttf", 120)
+
+    # Act
+    ImageDraw.ImageDraw.font = font
+
+    # Assert
+    try:
+        assert draw.getfont() == font
+    finally:
+        ImageDraw.ImageDraw.font = None
+        assert isinstance(draw.getfont(), ImageFont.ImageFont)
+
+
 def test_same_color_outline():
     # Prepare shape
     x0, y0 = 5, 5

src/PIL/ImageDraw.py

@@ -46,6 +46,8 @@
 
 
 class ImageDraw:
+    font = None
+
     def __init__(self, im, mode=None):
         """
         Create a drawing instance.
@@ -86,7 +88,6 @@ def __init__(self, im, mode=None):
         else:
             self.fontmode = "L"  # aliasing is okay for other modes
         self.fill = 0
-        self.font = None
 
     def getfont(self):
         """