Issue #7048: logb should round its result when that result doesn't fit

into the available precision.  (Tests for this change are included in
the most recent set of testcases from the Decimal Specification site;
those testcases will be updated shortly.)

Lib/decimal.py

@@ -3126,7 +3126,8 @@ class Decimal(object):
         # otherwise, simply return the adjusted exponent of self, as a
         # Decimal.  Note that no attempt is made to fit the result
         # into the current context.
-        return Decimal(self.adjusted())
+        ans = Decimal(self.adjusted())
+        return ans._fix(context)
 
     def _islogical(self):
         """Return True if self is a logical operand.

Misc/NEWS

@@ -398,6 +398,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #7048: Force Decimal.logb to round its result when that result
+  is too large to fit in the current precision.
+
 - Issue #6516: Added owner/group support when creating tar archives in 
   Distutils.