call __float__ on str subclasses #5759

tests by R. David Murray
diff --git a/Misc/NEWS b/Misc/NEWS
index 4c30c03..8577a9f 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -12,6 +12,8 @@
 Core and Builtins
 -----------------
 
+- Issue #5759: float() didn't call __float__ on str subclasses.
+
 - Issue #5704: the "-3" command-line option now implies "-t".
 
 - Issue #2170: refactored xml.dom.minidom.normalize, increasing both