diff --git a/python/sdist/amici/cxxcodeprinter.py b/python/sdist/amici/cxxcodeprinter.py
index 67d38a3a7a..2a5cb4b4a2 100644
--- a/python/sdist/amici/cxxcodeprinter.py
+++ b/python/sdist/amici/cxxcodeprinter.py
@@ -13,6 +13,8 @@
 from sympy.utilities.iterables import numbered_symbols
 from toposort import toposort
 
+from .import_utils import symbol_with_assumptions
+
 
 class AmiciCxxCodePrinter(CXX11CodePrinter):
     """
@@ -322,7 +324,7 @@ def csc_matrix(
     colnames: list[sp.Symbol],
     identifier: int | None = 0,
     pattern_only: bool | None = False,
-) -> tuple[list[int], list[int], sp.Matrix, list[str], sp.Matrix]:
+) -> tuple[list[int], list[int], sp.Matrix, list[sp.Symbol], sp.Matrix]:
     """
     Generates the sparse symbolic identifiers, symbolic identifiers,
     sparse matrix, column pointers and row values for a symbolic
@@ -371,11 +373,11 @@ def csc_matrix(
             symbol_name = f"d{rownames[row].name}_d{colnames[col].name}"
             if identifier:
                 symbol_name += f"_{identifier}"
-            symbol_list.append(symbol_name)
+            symbol_list.append(symbol_with_assumptions(symbol_name))
             if pattern_only:
                 continue
 
-            sparse_matrix[row, col] = sp.Symbol(symbol_name, real=True)
+            sparse_matrix[row, col] = symbol_with_assumptions(symbol_name)
             sparse_list.append(matrix[row, col])
 
     if idx == 0:
diff --git a/python/sdist/amici/de_export.py b/python/sdist/amici/de_export.py
index 7c6de98d9f..a8e8764956 100644
--- a/python/sdist/amici/de_export.py
+++ b/python/sdist/amici/de_export.py
@@ -399,7 +399,7 @@ def _write_index_files(self, name: str) -> None:
         lines = []
         for index, symbol in enumerate(symbols):
             symbol_name = strip_pysb(symbol)
-            if str(symbol) == "0":
+            if symbol.is_zero:
                 continue
             if str(symbol_name) == "":
                 raise ValueError(f'{name} contains a symbol called ""')
@@ -816,10 +816,11 @@ def _get_function_body(
             function in self.model.sym_names()
             and function not in non_unique_id_symbols
         ):
-            if function in sparse_functions:
-                symbols = list(map(sp.Symbol, self.model.sparsesym(function)))
-            else:
-                symbols = self.model.sym(function)
+            symbols = (
+                self.model.sparsesym(function)
+                if function in sparse_functions
+                else self.model.sym(function)
+            )
 
             if function in ("w", "dwdw", "dwdx", "dwdp"):
                 # Split into a block of static and dynamic expressions.
diff --git a/python/sdist/amici/de_model.py b/python/sdist/amici/de_model.py
index 829b99fe56..4aaead9770 100644
--- a/python/sdist/amici/de_model.py
+++ b/python/sdist/amici/de_model.py
@@ -143,7 +143,7 @@ class DEModel:
         model
 
     :ivar _sparsesyms:
-        carries linear list of all symbolic identifiers for sparsified
+        carries linear list of all symbols for sparsified
         variables
 
     :ivar _colptrs:
@@ -193,7 +193,7 @@ class DEModel:
         res and FIM make sense.
 
     :ivar _static_indices:
-        dict of lists list of indices of static variables for different
+        dict of lists of indices of static variables for different
         model entities.
 
     :ivar _z2event:
@@ -254,7 +254,9 @@ def __init__(
         self._vals: dict[str, list[sp.Expr]] = dict()
         self._names: dict[str, list[str]] = dict()
         self._syms: dict[str, sp.Matrix | list[sp.Matrix]] = dict()
-        self._sparsesyms: dict[str, list[str] | list[list[str]]] = dict()
+        self._sparsesyms: dict[
+            str, list[sp.Symbol] | list[list[sp.Symbol]]
+        ] = dict()
         self._colptrs: dict[str, list[int] | list[list[int]]] = dict()
         self._rowvals: dict[str, list[int] | list[list[int]]] = dict()
 
@@ -616,11 +618,11 @@ def add_conservation_law(
         variables.
 
         :param state:
-            symbolic identifier of the state that should be replaced by
+            Symbol of the state that should be replaced by
             the conservation law (:math:`x_j`)
 
         :param total_abundance:
-            symbolic identifier of the total abundance (:math:`T/a_j`)
+            Symbol of the total abundance (:math:`T/a_j`)
 
         :param coefficients:
             Dictionary of coefficients {x_i: a_i}
@@ -814,16 +816,18 @@ def sym(self, name: str) -> sp.Matrix:
             name of the symbolic variable
 
         :return:
-            matrix of symbolic identifiers
+            matrix of symbols
         """
         if name not in self._syms:
             self._generate_symbol(name)
 
         return self._syms[name]
 
-    def sparsesym(self, name: str, force_generate: bool = True) -> list[str]:
+    def sparsesym(
+        self, name: str, force_generate: bool = True
+    ) -> list[sp.Symbol]:
         """
-        Returns (and constructs if necessary) the sparsified identifiers for
+        Returns (and constructs if necessary) the sparsified symbols for
         a sparsified symbolic variable.
 
         :param name:
@@ -833,7 +837,7 @@ def sparsesym(self, name: str, force_generate: bool = True) -> list[str]:
             whether the symbols should be generated if not available
 
         :return:
-            linearized Matrix containing the symbolic identifiers
+            linearized Matrix containing the symbols
         """
         if name not in sparse_functions:
             raise ValueError(f"{name} is not marked as sparse")
@@ -1101,7 +1105,7 @@ def dynamic_indices(self, name: str) -> list[int]:
 
     def _generate_symbol(self, name: str) -> None:
         """
-        Generates the symbolic identifiers for a symbolic variable
+        Generates the symbols for a symbolic variable
 
         :param name:
             name of the symbolic variable
diff --git a/python/sdist/amici/de_model_components.py b/python/sdist/amici/de_model_components.py
index 4f12ec70be..a269338274 100644
--- a/python/sdist/amici/de_model_components.py
+++ b/python/sdist/amici/de_model_components.py
@@ -26,7 +26,9 @@
     "LogLikelihoodZ",
     "LogLikelihoodRZ",
     "ModelQuantity",
+    "NoiseParameter",
     "Observable",
+    "ObservableParameter",
     "Parameter",
     "SigmaY",
     "SigmaZ",
@@ -176,7 +178,7 @@ def get_ncoeff(self, state_id) -> sp.Expr | int | float:
         :param state_id:
             identifier of the state
 
-        :return: normalized coefficent of the state
+        :return: normalized coefficient of the state
         """
         return self._coefficients.get(state_id, 0.0) / self._ncoeff
 
@@ -404,7 +406,7 @@ def __init__(
         value: sp.Expr,
         measurement_symbol: sp.Symbol | None = None,
         transformation: None
-        | (ObservableTransformation) = ObservableTransformation.LIN,
+        | ObservableTransformation = ObservableTransformation.LIN,
     ):
         """
         Create a new Observable instance.
diff --git a/python/tests/test_ode_export.py b/python/tests/test_ode_export.py
index 6dc4d85f05..9e6917718e 100644
--- a/python/tests/test_ode_export.py
+++ b/python/tests/test_ode_export.py
@@ -3,6 +3,7 @@
 import sympy as sp
 from amici.cxxcodeprinter import csc_matrix
 from amici.testing import skip_on_valgrind
+from amici.import_utils import symbol_with_assumptions
 
 
 @skip_on_valgrind
@@ -24,7 +25,11 @@ def test_csc_matrix():
     assert symbol_col_ptrs == [0, 2, 3]
     assert symbol_row_vals == [0, 1, 1]
     assert sparse_list == sp.Matrix([[1], [2], [3]])
-    assert symbol_list == ["da1_db1", "da2_db1", "da2_db2"]
+    assert symbol_list == [
+        symbol_with_assumptions("da1_db1"),
+        symbol_with_assumptions("da2_db1"),
+        symbol_with_assumptions("da2_db2"),
+    ]
     assert str(sparse_matrix) == "Matrix([[da1_db1, 0], [da2_db1, da2_db2]])"
 
 
@@ -66,7 +71,10 @@ def test_csc_matrix_vector():
     assert symbol_col_ptrs == [0, 2]
     assert symbol_row_vals == [0, 1]
     assert sparse_list == sp.Matrix([[1], [2]])
-    assert symbol_list == ["da1_db", "da2_db"]
+    assert symbol_list == [
+        symbol_with_assumptions("da1_db"),
+        symbol_with_assumptions("da2_db"),
+    ]
     assert str(sparse_matrix) == "Matrix([[da1_db], [da2_db]])"
 
     # Test continuation of numbering of symbols
@@ -86,7 +94,7 @@ def test_csc_matrix_vector():
     assert symbol_col_ptrs == [0, 1]
     assert symbol_row_vals == [1]
     assert sparse_list == sp.Matrix([[3]])
-    assert symbol_list == ["da2_db_1"]
+    assert symbol_list == [symbol_with_assumptions("da2_db_1")]
     assert str(sparse_matrix) == "Matrix([[0], [da2_db_1]])"