corrections in fluid library to make call_lib pass again

- adapted wrong files for new biomethane properties
- added lhv and hhv with exception in case file was not found, as these properties are not absolutely necessary

pandapipes/properties/biomethane_treated/compressibility.txt

@@ -1,3 +1,3 @@
 # source: linear approximation based on CoolProp (http://www.coolprop.org/)
 # slope in 1/bar, offset for linear property
--0.0024789428559189412, 0.9962776221466679
+-0.0024789428559189412 0.9962776221466679

pandapipes/properties/biomethane_treated/heat_capacity.txt

@@ -1,6 +1,6 @@
 #source CoolProp (http://www.coolprop.org/)
 # temperature in Kelvin, isobaric heat capacity in J/(kg K)
-263.151976.8823234072695
+263.15 1976.8823234072695
 265.15 1980.6134982832095
 267.15 1984.416050463013
 269.15 1988.2894370033634

pandapipes/properties/fluids.py

@@ -680,24 +680,22 @@ def linear_property(prop):
 
     phase = "liquid" if fluid_name in _LIQUIDS else "gas"
 
-    density = interextra_property("density")
-    viscosity = interextra_property("viscosity")
-    heat_capacity = interextra_property("heat_capacity")
-    molar_mass = constant_property("molar_mass")
-    der_compr = constant_property("der_compressibility")
-    compr = linear_property("compressibility")
-
-    if (phase == 'gas') & (fluid_name != 'air'):
-        lhv = constant_property("lower_heating_value")
-        hhv = constant_property("higher_heating_value")
-
-        return Fluid(fluid_name, phase, density=density, viscosity=viscosity,
-                     heat_capacity=heat_capacity, molar_mass=molar_mass,
-                     compressibility=compr, der_compressibility=der_compr, lhv=lhv, hhv=hhv)
-    else:
-        return Fluid(fluid_name, phase, density=density, viscosity=viscosity,
-                     heat_capacity=heat_capacity, molar_mass=molar_mass, compressibility=compr,
-                     der_compressibility=der_compr)
+    properties = dict()
+    properties["density"] = interextra_property("density")
+    properties["viscosity"] = interextra_property("viscosity")
+    properties["heat_capacity"] = interextra_property("heat_capacity")
+    properties["molar_mass"] = constant_property("molar_mass")
+    properties["der_compressibility"] = constant_property("der_compressibility")
+    properties["compressibility"] = linear_property("compressibility")
+
+    if phase == 'gas':
+        for entry, name in [("lhv", "lower_heating_value"), ("hhv", "higher_heating_value")]:
+            try:
+                properties[entry] = constant_property(name)
+            except FileNotFoundError:
+                pass
+
+    return Fluid(fluid_name, phase, **properties)
 
 
 def get_fluid(net):