Fix unnecessary and harmful copy of pandas objects

CHANGELOG.md

@@ -11,12 +11,17 @@ In this file noteworthy changes of new releases of pyLife are documented since
 * Drop support for python-3.8 ast it is end of life
 
 
-### Minor improvments
+### Minor improvements
 
-* Connectivity information is now transfered from odbserver to odbclient as
+* Connectivity information is now transferred from odbserver to odbclient as
   ints.
 
 
+### Bugfixes
+
+* Fix unnecessary and harmful copy of pandas object in Wöhler classes (#146)
+
+
 ## pylife-2.1.3
 
 ### Improvements

src/pylife/materiallaws/woehlercurve.py

@@ -52,10 +52,6 @@ class WoehlerCurve(PylifeSignal):
                or calculated from ``TN`` if given.
     """
 
-    def __init__(self, pandas_obj):
-        self._obj = pandas_obj.copy()
-        self._validate()
-
     def _validate(self):
         self.fail_if_key_missing(['k_1', 'ND', 'SD'])
         self._k_2 = self._obj.get('k_2', np.inf)

src/pylife/strength/woehler_fkm_nonlinear.py

@@ -46,10 +46,6 @@ class WoehlerCurvePRAM(PylifeSignal):
     * ``P_RAM_D`` : The damage parameter value of the endurance limit of the component, computed as P_RAM_D_WS / f_RAM (FKM nonlinear, eq. 2.6-89)
     """
 
-    def __init__(self, pandas_obj):
-        self._obj = pandas_obj.copy()
-        self._validate()
-
     def _validate(self):
         self.fail_if_key_missing(['P_RAM_Z', 'P_RAM_D', 'd_1', 'd_2'])
 
@@ -195,13 +191,6 @@ class WoehlerCurvePRAJ(PylifeSignal):
     * ``P_RAJ_D_0`` : The initial load level of the endurance limit
     """
 
-    def __init__(self, pandas_obj):
-        self._obj = pandas_obj.copy()
-        self._validate()
-
-        # eq. (2.9-27)
-        self._P_RAJ_D = self._obj.P_RAJ_D_0
-
     def _validate(self):
         self.fail_if_key_missing(['P_RAJ_Z', 'P_RAJ_D_0', 'd_RAJ'])
 
@@ -212,6 +201,10 @@ def _validate(self):
         if self._obj.d_RAJ >= 0:
             raise ValueError(f"d_RAJ ({self._obj.d_RAJ}) has to be negative!")
 
+        # eq. (2.9-27)
+        self._P_RAJ_D = self._obj.P_RAJ_D_0
+
+
     def update_P_RAJ_D(self, P_RAJ_D):
         """This method is used to update the fatigue strength P_RAJ_D, which is stored in this woehler curve.
 

tests/materiallaws/test_woehlercurve.py

@@ -550,3 +550,19 @@ def test_load_is_basquin_load(SD, k_1, ND, cycles):
 def test_cycles_is_basquin_cycles(SD, k_1, ND, load):
     wc = WoehlerCurve.from_parameters(SD=SD, k_1=k_1, ND=ND)
     assert wc.cycles(load) == wc.basquin_cycles(load)
+
+
+def test_changed_TN():
+    wc = pd.Series({
+        'k_1': 7.,
+        'TN': 1.75,
+        'ND': 1e6,
+        'SD': 300.0
+    })
+
+    _ = wc.woehler
+
+    wc['TN'] = 1.48
+    new_wc = wc.woehler.to_pandas()
+
+    assert new_wc['TN'] == 1.48

tests/strength/test_woehler_fkm_nonlinear.py

@@ -151,6 +151,21 @@ def test_woehler_curve_P_RAM_exceptions(P_RAM_Z, P_RAM_D, d_1, d_2):
         component_woehler_curve_P_RAM = assessment_parameters.woehler_P_RAM
 
 
+def test_woehler_curve_P_RAM_change_params():
+    ap = pd.Series({
+        "P_RAM_Z": 400.0,
+        "P_RAM_D": 150.0,
+        "d_1": -0.3,
+        "d_2": -0.2
+    })
+
+    _ = ap.woehler_P_RAM
+
+    ap["d_2"] = -0.9
+
+    assert ap.woehler_P_RAM.to_pandas()["d_2"] == -0.9
+
+
 # ---------- P_RAJ --------------
 @pytest.mark.parametrize(
     "P_RAJ_Z, P_RAJ_D_0, d_RAJ", [
@@ -260,3 +275,17 @@ def test_woehler_curve_P_RAJ_exceptions(P_RAJ_Z, P_RAJ_D_0, d_RAJ):
 
     with pytest.raises(ValueError, match="has to be"):
         component_woehler_curve_P_RAJ = assessment_parameters.woehler_P_RAJ
+
+
+def test_woehler_curve_P_RAJ_change_params():
+    ap = pd.Series({
+        "P_RAJ_Z": 150.0,
+        "P_RAJ_D_0": 0.1,
+        "d_RAJ": -0.5,
+    })
+
+    _ = ap.woehler_P_RAJ
+
+    ap["d_RAJ"] = -0.7
+
+    assert ap.woehler_P_RAJ.to_pandas()["d_RAJ"] == -0.7