diff --git a/parcels/field.py b/parcels/field.py
index 952c8965fe..075eefcc09 100644
--- a/parcels/field.py
+++ b/parcels/field.py
@@ -548,9 +548,6 @@ def from_netcdf(
         if "time" in indices:
             logger.warning_once("time dimension in indices is not necessary anymore. It is then ignored.")
 
-        if "full_load" in kwargs:  # for backward compatibility with Parcels < v2.0.0
-            deferred_load = not kwargs["full_load"]
-
         if grid.time.size <= 2:
             deferred_load = False
 
diff --git a/parcels/interaction/interactionkernel.py b/parcels/interaction/interactionkernel.py
index db4c7f8975..a02742abbf 100644
--- a/parcels/interaction/interactionkernel.py
+++ b/parcels/interaction/interactionkernel.py
@@ -1,5 +1,4 @@
 import inspect
-import sys
 from collections import defaultdict
 
 import numpy as np
@@ -113,10 +112,7 @@ def check_kernel_signature_on_version(self):
         numkernelargs = []
         if self._pyfunc is not None and isinstance(self._pyfunc, list):
             for func in self._pyfunc:
-                if sys.version_info[0] < 3:
-                    numkernelargs.append(len(inspect.getargspec(func).args))
-                else:
-                    numkernelargs.append(len(inspect.getfullargspec(func).args))
+                numkernelargs.append(len(inspect.getfullargspec(func).args))
         return numkernelargs
 
     def remove_lib(self):
diff --git a/parcels/kernel.py b/parcels/kernel.py
index 37578af71f..097a777a88 100644
--- a/parcels/kernel.py
+++ b/parcels/kernel.py
@@ -233,9 +233,10 @@ def __init__(
 
         numkernelargs = self.check_kernel_signature_on_version()
 
-        assert (
-            numkernelargs == 3
-        ), "Since Parcels v2.0, kernels do only take 3 arguments: particle, fieldset, time !! AND !! Argument order in field interpolation is time, depth, lat, lon."
+        if numkernelargs != 3:
+            raise ValueError(
+                "Since Parcels v2.0, kernels do only take 3 arguments: particle, fieldset, time !! AND !! Argument order in field interpolation is time, depth, lat, lon."
+            )
 
         self.name = f"{ptype.name}{self.funcname}"
 
@@ -324,7 +325,7 @@ def Updatecoords(particle, fieldset, time):
             particle.depth_nextloop = particle.depth + particle_ddepth  # noqa
             particle.time_nextloop = particle.time + particle.dt
 
-        self._pyfunc = self.__radd__(Setcoords).__add__(Updatecoords)._pyfunc
+        self._pyfunc = (Setcoords + self + Updatecoords)._pyfunc
 
     def check_fieldsets_in_kernels(self, pyfunc):
         """
@@ -382,13 +383,10 @@ def check_fieldsets_in_kernels(self, pyfunc):
                     self.fieldset.add_constant("RK45_max_dt", 60 * 60 * 24)
 
     def check_kernel_signature_on_version(self):
-        numkernelargs = 0
-        if self._pyfunc is not None:
-            if sys.version_info[0] < 3:
-                numkernelargs = len(inspect.getargspec(self._pyfunc).args)
-            else:
-                numkernelargs = len(inspect.getfullargspec(self._pyfunc).args)
-        return numkernelargs
+        """Returns number of arguments in a Python function."""
+        if self._pyfunc is None:
+            return 0
+        return len(inspect.getfullargspec(self._pyfunc).args)
 
     def remove_lib(self):
         if self._lib is not None: