Remove code duplication by moving the draw function into the drawing module

Author: hyanwong

python/tskit/drawing.py

@@ -894,6 +894,13 @@ def __init__(
         self.dwg_base = dwg.add(dwg.g(class_=svg_class))
         self.drawing = dwg
 
+    def draw(self, path=None):
+        output = self.drawing.tostring()
+        if path is not None:
+            # TODO remove the 'pretty' when we are done debugging this.
+            self.drawing.saveas(path, pretty=True)
+        return SVGString(output)
+
     def get_plotbox(self):
         """
         Get the svgwrite plotbox, creating it if necessary.

python/tskit/trees.py

@@ -1964,7 +1964,7 @@ def draw_svg(
         :return: An SVG representation of a tree.
         :rtype: SVGString
         """
-        draw = drawing.SvgTree(
+        d = drawing.SvgTree(
             self,
             size,
             time_scale=time_scale,
@@ -1995,11 +1995,7 @@ def draw_svg(
             preamble=preamble,
             **kwargs,
         )
-        output = draw.drawing.tostring()
-        if path is not None:
-            # TODO: removed the pretty here when this is stable.
-            draw.drawing.saveas(path, pretty=True)
-        return drawing.SVGString(output)
+        return d.draw(path)
 
     def draw(
         self,
@@ -7599,7 +7595,7 @@ def draw_svg(
             strictly within an empty region then that tree will not be plotted on the
             right hand side, and the X axis will end at ``empty_tree.interval.left``
         """
-        draw = drawing.SvgTreeSequence(
+        d = drawing.SvgTreeSequence(
             self,
             size,
             x_scale=x_scale,
@@ -7629,11 +7625,7 @@ def draw_svg(
             preamble=preamble,
             **kwargs,
         )
-        output = draw.drawing.tostring()
-        if path is not None:
-            # TODO remove the 'pretty' when we are done debugging this.
-            draw.drawing.saveas(path, pretty=True)
-        return drawing.SVGString(output)
+        return d.draw(path)
 
     def draw_text(
         self,