Issue #21812: Trigger immediate transformation in turtle.shapetransform().

Lib/turtle.py

@@ -2945,7 +2945,7 @@ class RawTurtle(TPen, TNavigator):
         self._stretchfactor = a11, a22
         self._shearfactor = a12/a22
         self._tilt = alfa
-        self._update()
+        self.pen(resizemode="user")
 
 
     def _polytrafo(self, poly):

Misc/ACKS

@@ -235,6 +235,7 @@ Ingrid Cheung
 Albert Chin-A-Young
 Adal Chiriliuc
 Matt Chisholm
+Lita Cho
 Anders Chrigström
 Tom Christiansen
 Vadim Chugunov

Misc/NEWS

@@ -29,6 +29,9 @@ Library
 
 - Issue #21491: socketserver: Fix a race condition in child processes reaping.
 
+- Issue #21812: turtle.shapetransform did not tranform the turtle on the
+  first call.  (Issue identified and fixed by Lita Cho.)
+
 - Issue #21635:  The difflib SequenceMatcher.get_matching_blocks() method
   cache didn't match the actual result.  The former was a list of tuples
   and the latter was a list of named tuples.