diff --git a/openfisca_core/taxscales.py b/openfisca_core/taxscales.py
index eadbd5d535..15b57ad3af 100644
--- a/openfisca_core/taxscales.py
+++ b/openfisca_core/taxscales.py
@@ -1,5 +1,3 @@
-from __future__ import annotations
-
 import copy
 import itertools
 import logging
@@ -11,7 +9,6 @@
 from numpy import (
     around,
     array,
-    asarray,
     digitize,
     dot,
     finfo,
@@ -44,7 +41,7 @@ def __init__(
             class_name: str,
             method_name: str,
             arg_name: str,
-            arg_value: Union[List, ndarray]
+            arg_value: ndarray
             ) -> None:
         message = [
             f"'{class_name}.{method_name}' can't be run with an empty '{arg_name}':\n",
@@ -109,7 +106,7 @@ def __repr__(self) -> Any:
             f"{self.__class__.__name__}",
             )
 
-    def calc(self, _tax_base: Union[ndarray[int], ndarray[float]], _right: bool) -> Any:
+    def calc(self, _tax_base: ndarray, _right: bool) -> Any:
         raise NotImplementedError(
             "Method 'calc' is not implemented for "
             f"{self.__class__.__name__}",
@@ -129,7 +126,7 @@ def multiply_thresholds(
 
     def bracket_indices(
             self,
-            tax_base: Union[ndarray[int], ndarray[float]],
+            tax_base: ndarray,
             factor: float = 1.0,
             round_base_decimals: Optional[int] = None,
             ) -> Any:
@@ -247,20 +244,20 @@ def multiply_thresholds(
 
     def bracket_indices(
             self,
-            tax_base: Union[ndarray[int], ndarray[float]],
+            tax_base: ndarray,
             factor: float = 1.0,
             round_decimals: Optional[int] = None,
-            ) -> ndarray[int]:
+            ) -> ndarray:
         """
         Compute the relevant bracket indices for the given tax bases.
 
-        :param ndarray tax_base: Array of the tax bases.
-        :param float factor: Factor to apply to the thresholds of the tax scales.
-        :param int round_decimals: Decimals to keep when rounding thresholds.
+        :param tax_base: Array of the tax bases.
+        :param factor: Factor to apply to the thresholds of the tax scales.
+        :param round_decimals: Decimals to keep when rounding thresholds.
 
         :returns: Int array with relevant bracket indices for the given tax bases.
 
-        For instance:
+        :example:
 
         >>> tax_scale = AbstractRateTaxScale()
         >>> tax_scale.add_bracket(0, 0)
@@ -278,7 +275,7 @@ def bracket_indices(
                 self.thresholds,
                 )
 
-        if not size(asarray(tax_base)):
+        if not size(array(tax_base)):
             raise EmptyArgumentError(
                 self.__class__.__name__,
                 "bracket_indices",
@@ -342,11 +339,7 @@ def add_bracket(self, threshold: int, amount: Union[int, float]) -> None:
             self.thresholds.insert(i, threshold)
             self.amounts.insert(i, amount)
 
-    def calc(
-            self,
-            tax_base: Union[ndarray[int], ndarray[float]],
-            right: bool = False,
-            ) -> ndarray[float]:
+    def calc(self, tax_base: ndarray, right: bool = False) -> ndarray:
         guarded_thresholds = array([-inf] + self.thresholds + [inf])
         bracket_indices = digitize(tax_base, guarded_thresholds, right = right)
         guarded_amounts = array([0] + self.amounts + [0])
@@ -366,11 +359,7 @@ class MarginalAmountTaxScale(SingleAmountTaxScale):
     containing the input.
     """
 
-    def calc(
-            self,
-            tax_base: Union[ndarray[int], ndarray[float]],
-            _right: bool = False,
-            ) -> ndarray[float]:
+    def calc(self, tax_base: ndarray, _right: bool = False) -> ndarray:
         base1 = tile(tax_base, (len(self.thresholds), 1)).T
         thresholds1 = tile(hstack((self.thresholds, inf)), (len(tax_base), 1))
         a = max_(min_(base1, thresholds1[:, 1:]) - thresholds1[:, :-1], 0)
@@ -378,11 +367,7 @@ def calc(
 
 
 class LinearAverageRateTaxScale(AbstractRateTaxScale):
-    def calc(
-            self,
-            tax_base: Union[ndarray[int], ndarray[float]],
-            _right: bool = False,
-            ) -> ndarray[float]:
+    def calc(self, tax_base: ndarray, _right: bool = False) -> ndarray:
         if len(self.rates) == 1:
             return tax_base * self.rates[0]
 
@@ -460,20 +445,20 @@ def add_tax_scale(self, tax_scale: AbstractRateTaxScale) -> None:
 
     def calc(
             self,
-            tax_base: Union[ndarray[int], ndarray[float]],
+            tax_base: ndarray,
             factor: float = 1.0,
             round_base_decimals: Optional[int] = None,
-            ) -> ndarray[float]:
+            ) -> ndarray:
         """
         Compute the tax amount for the given tax bases by applying the taxscale.
 
-        :param ndarray tax_base: Array of the tax bases.
-        :param float factor: Factor to apply to the thresholds of the tax scale.
-        :param int round_base_decimals: Decimals to keep when rounding thresholds.
+        :param tax_base: Array of the tax bases.
+        :param factor: Factor to apply to the thresholds of the tax scale.
+        :param round_base_decimals: Decimals to keep when rounding thresholds.
 
         :returns: Float array with tax amount for the given tax bases.
 
-        For instance:
+        :example:
 
         >>> tax_scale = MarginalRateTaxScale()
         >>> tax_scale.add_bracket(0, 0)
@@ -529,20 +514,20 @@ def combine_bracket(
 
     def marginal_rates(
             self,
-            tax_base: Union[ndarray[int], ndarray[float]],
+            tax_base: ndarray,
             factor: float = 1.0,
             round_base_decimals: Optional[int] = None,
-            ) -> ndarray[float]:
+            ) -> ndarray:
         """
         Compute the marginal tax rates relevant for the given tax bases.
 
-        :param ndarray tax_base: Array of the tax bases.
-        :param float factor: Factor to apply to the thresholds of the tax scale.
-        :param int round_base_decimals: Decimals to keep when rounding thresholds.
+        :param tax_base: Array of the tax bases.
+        :param factor: Factor to apply to the thresholds of the tax scale.
+        :param round_base_decimals: Decimals to keep when rounding thresholds.
 
         :returns: Float array with relevant marginal tax rate for the given tax bases.
 
-        For instance:
+        :example:
 
         >>> tax_scale = MarginalRateTaxScale()
         >>> tax_scale.add_bracket(0, 0)