Remove outdated v3 code

src/parcels/_core/field.py

@@ -22,6 +22,7 @@
 from parcels._core.utils.time import TimeInterval
 from parcels._core.uxgrid import UxGrid
 from parcels._core.xgrid import XGrid, _transpose_xfield_data_to_tzyx
+from parcels._python import assert_same_function_signature
 from parcels._reprs import default_repr
 from parcels._typing import VectorType
 from parcels.interpolators import (
@@ -30,7 +31,6 @@
     ZeroInterpolator,
     ZeroInterpolator_Vector,
 )
-from parcels.utils._helpers import _assert_same_function_signature
 
 __all__ = ["Field", "VectorField"]
 
@@ -139,7 +139,7 @@ def __init__(
         if interp_method is None:
             self._interp_method = _DEFAULT_INTERPOLATOR_MAPPING[type(self.grid)]
         else:
-            _assert_same_function_signature(interp_method, ref=ZeroInterpolator, context="Interpolation")
+            assert_same_function_signature(interp_method, ref=ZeroInterpolator, context="Interpolation")
             self._interp_method = interp_method
 
         self.igrid = -1  # Default the grid index to -1
@@ -195,7 +195,7 @@ def interp_method(self):
 
     @interp_method.setter
     def interp_method(self, method: Callable):
-        _assert_same_function_signature(method, ref=ZeroInterpolator, context="Interpolation")
+        assert_same_function_signature(method, ref=ZeroInterpolator, context="Interpolation")
         self._interp_method = method
 
     def _check_velocitysampling(self):
@@ -270,7 +270,7 @@ def __init__(
         if vector_interp_method is None:
             self._vector_interp_method = None
         else:
-            _assert_same_function_signature(vector_interp_method, ref=ZeroInterpolator_Vector, context="Interpolation")
+            assert_same_function_signature(vector_interp_method, ref=ZeroInterpolator_Vector, context="Interpolation")
             self._vector_interp_method = vector_interp_method
 
     def __repr__(self):
@@ -286,7 +286,7 @@ def vector_interp_method(self):
 
     @vector_interp_method.setter
     def vector_interp_method(self, method: Callable):
-        _assert_same_function_signature(method, ref=ZeroInterpolator_Vector, context="Interpolation")
+        assert_same_function_signature(method, ref=ZeroInterpolator_Vector, context="Interpolation")
         self._vector_interp_method = method
 
     def eval(self, time: datetime, z, y, x, particles=None, applyConversion=True):

src/parcels/_core/kernel.py

@@ -17,12 +17,12 @@
     _raise_outside_time_interval_error,
 )
 from parcels._core.warnings import KernelWarning
+from parcels._python import assert_same_function_signature
 from parcels.kernels import (
     AdvectionAnalytical,
     AdvectionRK4,
     AdvectionRK45,
 )
-from parcels.utils._helpers import _assert_same_function_signature
 
 if TYPE_CHECKING:
     from collections.abc import Callable
@@ -67,7 +67,7 @@ def __init__(
         for f in pyfuncs:
             if not isinstance(f, types.FunctionType):
                 raise TypeError(f"Argument pyfunc should be a function or list of functions. Got {type(f)}")
-            _assert_same_function_signature(f, ref=AdvectionRK4, context="Kernel")
+            assert_same_function_signature(f, ref=AdvectionRK4, context="Kernel")
 
         if len(pyfuncs) == 0:
             raise ValueError("List of `pyfuncs` should have at least one function.")

src/parcels/_core/particlefile.py

@@ -15,7 +15,7 @@
 
 import parcels
 from parcels._core.particle import _SAME_AS_FIELDSET_TIME_INTERVAL, ParticleClass
-from parcels.utils._helpers import timedelta_to_float
+from parcels._core.utils.time import timedelta_to_float
 
 if TYPE_CHECKING:
     from parcels._core.particle import Variable

src/parcels/_core/utils/time.py

@@ -144,3 +144,12 @@ def maybe_convert_python_timedelta_to_numpy(dt: timedelta | np.timedelta64) -> n
             return np.timedelta64(0, "s")
     except Exception as e:
         raise ValueError(f"Could not convert {dt!r} to np.timedelta64.") from e
+
+
+def timedelta_to_float(dt: float | timedelta | np.timedelta64) -> float:
+    """Convert a timedelta to a float in seconds."""
+    if isinstance(dt, timedelta):
+        return dt.total_seconds()
+    if isinstance(dt, np.timedelta64):
+        return float(dt / np.timedelta64(1, "s"))
+    return float(dt)