Revert previous changes to frontend API

src/pystencils/sympyextensions/fast_approximation.py

@@ -2,7 +2,8 @@ from typing import List, Union
 
 import sympy as sp
 
-from pystencils.sympyextensions import AssignmentCollection, Assignment
+from ..assignment import Assignment
+from ..simp import AssignmentCollection
 
 
 # noinspection PyPep8Naming

src/pystencils/sympyextensions/math.py

@@ -10,7 +10,7 @@ from sympy import PolynomialError
 from sympy.functions import Abs
 from sympy.core.numbers import Zero
 
-from .astnodes import Assignment
+from ..assignment import Assignment
 from .typed_sympy import CastFunc, FieldPointerSymbol
 from ..types import PsPointerType, PsVectorType
 

tests/nbackend/kernelcreation/test_domain_kernels.py

@@ -2,7 +2,7 @@ import sympy as sp
 import numpy as np
 
 from pystencils import fields, Field, AssignmentCollection
-from pystencils.sympyextensions.astnodes import assignment_from_stencil
+from pystencils.assignment import assignment_from_stencil
 
 from pystencils.kernelcreation import create_kernel
 

tests/symbolics/test_address_of.py

@@ -6,7 +6,7 @@ import pystencils
 from pystencils.types import PsPointerType, create_type
 from pystencils.sympyextensions.pointers import AddressOf
 from pystencils.sympyextensions.typed_sympy import CastFunc
-from pystencils.sympyextensions import sympy_cse
+from pystencils.simp import sympy_cse
 
 import sympy as sp
 

tests/symbolics/test_conditional_field_access.py

@@ -16,7 +16,7 @@ import sympy as sp
 import pystencils as ps
 from pystencils import Field, x_vector
 from pystencils.sympyextensions.astnodes import ConditionalFieldAccess
-from pystencils.sympyextensions import sympy_cse
+from pystencils.simp import sympy_cse
 
 
 def add_fixed_constant_boundary_handling(assignments, with_cse):

tests/test_fvm.py

@@ -3,7 +3,7 @@ import pystencils as ps
 import numpy as np
 import pytest
 from itertools import product
-from pystencils.sympyextensions.rng import random_symbol
+from pystencils.rng import random_symbol
 from pystencils.sympyextensions.astnodes import SympyAssignment
 from pystencils.node_collection import NodeCollection
 

tests/test_random.py

@@ -5,7 +5,7 @@ import pytest
 import pystencils as ps
 from pystencils.sympyextensions.astnodes import SympyAssignment
 from pystencils.node_collection import NodeCollection
-from pystencils.sympyextensions.rng import PhiloxFourFloats, PhiloxTwoDoubles, AESNIFourFloats, AESNITwoDoubles, random_symbol
+from pystencils.rng import PhiloxFourFloats, PhiloxTwoDoubles, AESNIFourFloats, AESNITwoDoubles, random_symbol
 from pystencils.backends.simd_instruction_sets import get_supported_instruction_sets
 from pystencils.cpu.cpujit import get_compiler_config
 from pystencils.typing import TypedSymbol