From 8a62a9711525cf1e0193e3ec448d653b090de979 Mon Sep 17 00:00:00 2001
From: Jonathan Shimwell <mail@jshimwell.com>
Date: Fri, 6 Feb 2026 17:23:11 +0100
Subject: [PATCH] openmc.Tally creation from constructor (#3777)

---
 openmc/tallies.py              | 29 ++++++++++++++++++++++++++++-
 tests/unit_tests/test_tally.py | 19 +++++++++++++++++++
 2 files changed, 47 insertions(+), 1 deletion(-)
 create mode 100644 tests/unit_tests/test_tally.py

diff --git a/openmc/tallies.py b/openmc/tallies.py
index 74d4722af4..151add2bee 100644
--- a/openmc/tallies.py
+++ b/openmc/tallies.py
@@ -50,6 +50,18 @@ class Tally(IDManagerMixin):
         will automatically be assigned
     name : str, optional
         Name of the tally. If not specified, the name is the empty string.
+    scores : list of str, optional
+        List of scores, e.g. ['flux', 'fission']
+    filters : list of openmc.Filter, optional
+        List of filters for the tally
+    nuclides : list of str, optional
+        List of nuclides to score results for
+    estimator : {'analog', 'tracklength', 'collision'}, optional
+        Type of estimator for the tally
+    triggers : list of openmc.Trigger, optional
+        List of tally triggers
+    derivative : openmc.TallyDerivative, optional
+        A material perturbation derivative to apply to all scores in the tally
 
     Attributes
     ----------
@@ -124,7 +136,9 @@ class Tally(IDManagerMixin):
     next_id = 1
     used_ids = set()
 
-    def __init__(self, tally_id=None, name=''):
+    def __init__(self, tally_id=None, name='', scores=None, filters=None,
+                 nuclides=None, estimator=None, triggers=None,
+                 derivative=None):
         # Initialize Tally class attributes
         self.id = tally_id
         self.name = name
@@ -155,6 +169,19 @@ class Tally(IDManagerMixin):
         self._sp_filename = None
         self._results_read = False
 
+        if filters is not None:
+            self.filters = filters
+        if nuclides is not None:
+            self.nuclides = nuclides
+        if scores is not None:
+            self.scores = scores
+        if estimator is not None:
+            self.estimator = estimator
+        if triggers is not None:
+            self.triggers = triggers
+        if derivative is not None:
+            self.derivative = derivative
+
     def __eq__(self, other):
         if other.id != self.id:
             return False
diff --git a/tests/unit_tests/test_tally.py b/tests/unit_tests/test_tally.py
new file mode 100644
index 0000000000..52647a36c7
--- /dev/null
+++ b/tests/unit_tests/test_tally.py
@@ -0,0 +1,19 @@
+import openmc
+
+
+def test_tally_init_args():
+    """Test that Tally constructor kwargs are applied correctly."""
+    filter = openmc.EnergyFilter([0.0, 1.0, 20.0e6])
+    tally = openmc.Tally(
+        name='my tally',
+        scores=['flux', 'fission'],
+        filters=[filter],
+        nuclides=['U235'],
+        estimator='tracklength',
+    )
+
+    assert tally.name == 'my tally'
+    assert tally.scores == ['flux', 'fission']
+    assert tally.filters == [filter]
+    assert tally.nuclides == ['U235']
+    assert tally.estimator == 'tracklength'