[2.7] bpo-31500: IDLE: Scale default fonts on HiDPI displays. (GH-3639)

Lib/idlelib/FileList.py

@@ -107,8 +107,10 @@ def canonize(self, filename):
 
 def _test():
     from idlelib.EditorWindow import fixwordbreaks
+    from idlelib.run import fix_scaling
     import sys
     root = Tk()
+    fix_scaling(root)
     fixwordbreaks(root)
     root.withdraw()
     flist = FileList(root)

Lib/idlelib/PyShell.py

@@ -1552,6 +1552,8 @@ def main():
     # start editor and/or shell windows:
     root = Tk(className="Idle")
     root.withdraw()
+    from idlelib.run import fix_scaling
+    fix_scaling(root)
 
     # set application icon
     icondir = os.path.join(os.path.dirname(__file__), 'Icons')

Lib/idlelib/run.py

@@ -155,6 +155,7 @@ def show_socket_error(err, address):
     import Tkinter
     import tkMessageBox
     root = Tkinter.Tk()
+    fix_scaling(root)
     root.withdraw()
     if err.args[0] == 61: # connection refused
         msg = "IDLE's subprocess can't connect to %s:%d.  This may be due "\
@@ -240,6 +241,19 @@ def exit():
     capture_warnings(False)
     sys.exit(0)
 
+
+def fix_scaling(root):
+    """Scale fonts on HiDPI displays."""
+    import tkFont
+    scaling = float(root.tk.call('tk', 'scaling'))
+    if scaling > 1.4:
+        for name in tkFont.names(root):
+            font = tkFont.Font(root=root, name=name, exists=True)
+            size = int(font['size'])
+            if size < 0:
+                font['size'] = int(round(-0.75*size))
+
+
 class MyRPCServer(rpc.RPCServer):
 
     def handle_error(self, request, client_address):

Misc/NEWS.d/next/IDLE/2017-09-18-10-43-03.bpo-31500.Y_YDxA.rst

@@ -0,0 +1 @@
+Default fonts now are scaled on HiDPI displays.