From e36a66f17f21245bc88f5ebb1a8588e7e3737fe7 Mon Sep 17 00:00:00 2001
From: Philipp Arras <c@philipp-arras.de>
Date: Tue, 4 Feb 2025 21:21:01 +0100
Subject: [PATCH] DiagonalOperator: fixup

---
 src/operators/diagonal_operator.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/operators/diagonal_operator.py b/src/operators/diagonal_operator.py
index 670e97221..557878278 100644
--- a/src/operators/diagonal_operator.py
+++ b/src/operators/diagonal_operator.py
@@ -94,7 +94,8 @@ class DiagonalOperator(EndomorphicOperator):
                 raise ValueError("spaces and domain must have the same length")
             for i, j in enumerate(self._spaces):
                 if diagonal.domain[i] != self._domain[j]:
-                    raise ValueError("Mismatch:\n{diagonal.domain[i]}\n{self._domain[j]}")
+                    raise ValueError(f"Mismatch between:\n{diagonal.domain[i]}\n"
+                                     f"and:\n{self._domain[j]}")
             if self._spaces == tuple(range(len(self._domain))):
                 self._spaces = None  # shortcut
 
-- 
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