Merge pull request #8807 from eric-wieser/poly1d-fixes-fixes-fixes

TST: Prove that poly1d coeffs are immutable

2 files changed, 16 insertions, 3 deletions

diff --git a/numpy/lib/polynomial.py b/numpy/lib/polynomial.py
index e18bbc8bc..f49b7e295 100644
--- a/numpy/lib/polynomial.py
+++ b/numpy/lib/polynomial.py
@@ -1040,7 +1040,7 @@ class poly1d(object):
 
     @property
     def coeffs(self):
-        """ The polynomial coefficients """
+        """ A copy of the polynomial coefficients """
         return self._coeffs.copy()
 
     @property
@@ -1060,8 +1060,7 @@ class poly1d(object):
         return roots(self._coeffs)
 
     # our internal _coeffs property need to be backed by __dict__['coeffs'] for
-    # scipy to work correctly. Note that as a result, the getter for .coeffs
-    # does not run unless accessed through one of its aliases.
+    # scipy to work correctly.
     @property
     def _coeffs(self):
         return self.__dict__['coeffs']
diff --git a/numpy/lib/tests/test_polynomial.py b/numpy/lib/tests/test_polynomial.py
index f1e4543bb..0725c186d 100644
--- a/numpy/lib/tests/test_polynomial.py
+++ b/numpy/lib/tests/test_polynomial.py
@@ -222,6 +222,20 @@ class TestDocs(TestCase):
         assert_equal(p == p2, False)
         assert_equal(p != p2, True)
 
+    def test_poly_coeffs_immutable(self):
+        """ Coefficients should not be modifiable """
+        p = np.poly1d([1, 2, 3])
+
+        try:
+            # despite throwing an exception, this used to change state
+            p.coeffs += 1
+        except Exception:
+            pass
+        assert_equal(p.coeffs, [1, 2, 3])
+
+        p.coeffs[2] += 10
+        assert_equal(p.coeffs, [1, 2, 3])
+
 
 if __name__ == "__main__":
     run_module_suite()