From 3d809aed7b7b6af5c371bab68666857087335af9 Mon Sep 17 00:00:00 2001
From: Martin Trigaux <me@mart-e.be>
Date: Fri, 11 Jun 2021 18:49:30 +0200
Subject: raise error on missing single placeholder

---
 CHANGES.rst                | 3 +++
 src/markupsafe/__init__.py | 7 ++++++-
 tests/test_markupsafe.py   | 6 ++++++
 3 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/CHANGES.rst b/CHANGES.rst
index 9d19bc8..e15be20 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -3,6 +3,9 @@ Version 2.1.0
 
 Unreleased
 
+-   Raise error on missing single placeholder during string
+    interpolation. :issue:`225`
+
 
 Version 2.0.2
 -------------
diff --git a/src/markupsafe/__init__.py b/src/markupsafe/__init__.py
index 048ddb8..d1bf187 100644
--- a/src/markupsafe/__init__.py
+++ b/src/markupsafe/__init__.py
@@ -102,9 +102,14 @@ class Markup(str):
 
     def __mod__(self, arg: t.Any) -> "Markup":
         if isinstance(arg, tuple):
+            # a tuple of arguments, each wrapped
             arg = tuple(_MarkupEscapeHelper(x, self.escape) for x in arg)
-        else:
+        elif hasattr(type(arg), "__getitem__") and not isinstance(arg, str):
+            # a mapping of arguments, wrapped
             arg = _MarkupEscapeHelper(arg, self.escape)
+        else:
+            # a single argument, wrapped with the helper and a tuple
+            arg = (_MarkupEscapeHelper(arg, self.escape),)
 
         return self.__class__(super().__mod__(arg))
 
diff --git a/tests/test_markupsafe.py b/tests/test_markupsafe.py
index fcd9347..1d4ac2e 100644
--- a/tests/test_markupsafe.py
+++ b/tests/test_markupsafe.py
@@ -45,6 +45,12 @@ def test_html_interop():
     assert result == "<strong><em>awesome</em></strong>"
 
 
+@pytest.mark.parametrize("args", ["foo", 42, ("foo", 42)])
+def test_missing_interpol(args):
+    with pytest.raises(TypeError):
+        Markup("<em></em>") % args
+
+
 def test_tuple_interpol():
     result = Markup("<em>%s:%s</em>") % ("<foo>", "<bar>")
     expect = Markup("<em>&lt;foo&gt;:&lt;bar&gt;</em>")
-- 
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