bpo-34333: Fix %-formatting in Path.with_suffix() (GH-8663)

(cherry picked from commit 423d05f) Co-authored-by: Berker Peksag <berker.peksag@gmail.com>

Author: miss-islington

Lib/pathlib.py

@@ -813,7 +813,7 @@ def with_suffix(self, suffix):
  """
  f = self._flavour
  if f.sep in suffix or f.altsep and f.altsep in suffix:
- raise ValueError("Invalid suffix %r" % (suffix))
+ raise ValueError("Invalid suffix %r" % (suffix,))
  if suffix and not suffix.startswith('.') or suffix == '.':
  raise ValueError("Invalid suffix %r" % (suffix))
  name = self.name

Lib/test/test_pathlib.py

@@ -577,6 +577,8 @@ def test_with_suffix_common(self):
  self.assertRaises(ValueError, P('a/b').with_suffix, '.c/.d')
  self.assertRaises(ValueError, P('a/b').with_suffix, './.d')
  self.assertRaises(ValueError, P('a/b').with_suffix, '.d/.')
+ self.assertRaises(ValueError, P('a/b').with_suffix,
+ (self.flavour.sep, 'd'))
 
  def test_relative_to_common(self):
  P = self.cls

Misc/NEWS.d/next/Library/2018-08-04-00-06-28.bpo-34333.5NHG93.rst

@@ -0,0 +1,2 @@
+Fix %-formatting in :meth:`pathlib.PurePath.with_suffix` when formatting an
+error message.