diff --git a/probability.py b/probability.py
index e102e4dd8..347efc7bd 100644
--- a/probability.py
+++ b/probability.py
@@ -72,10 +72,10 @@ def normalize(self):
                 self.prob[val] /= total
         return self
 
-    def show_approx(self, numfmt='%.3g'):
+    def show_approx(self, numfmt='{:.3g}'):
         """Show the probabilities rounded and sorted by key, for the
         sake of portable doctests."""
-        return ', '.join([('%s: ' + numfmt) % (v, p)
+        return ', '.join([('{}: ' + numfmt).format(v, p)
                           for (v, p) in sorted(self.prob.items())])
 
     def __repr__(self):
diff --git a/utils.py b/utils.py
index ed44f1e9e..43aaeec04 100644
--- a/utils.py
+++ b/utils.py
@@ -307,10 +307,10 @@ def issequence(x):
     return isinstance(x, collections.abc.Sequence)
 
 
-def print_table(table, header=None, sep='   ', numfmt='%g'):
+def print_table(table, header=None, sep='   ', numfmt='{}'):
     """Print a list of lists as a table, so that columns line up nicely.
     header, if specified, will be printed as the first row.
-    numfmt is the format for all numbers; you might want e.g. '%6.2f'.
+    numfmt is the format for all numbers; you might want e.g. '{:.2f}'.
     (If you want different formats in different columns,
     don't use print_table.) sep is the separator between columns."""
     justs = ['rjust' if isnumber(x) else 'ljust' for x in table[0]]