I figured out how to fill out in the cardioid

drawing.py

@@ -2,7 +2,9 @@ from turtle import (
     right,
     color,
     goto,
-    pensize
+    pensize,
+    begin_fill,
+    end_fill
 )
 from math import sin, cos, tau, pi
 
@@ -22,7 +24,9 @@ segments = 50
 coords = get_segmented_cardioid(segments)
 color(1, 0, 0)
 pensize(5)
+begin_fill()
 for i in range(segments + 1):
     goto(coords[i])
 right(90)
+end_fill()
 input()