feat: add attribute min_value, max_value in variable.py

changelog_entry.yaml

@@ -0,0 +1,4 @@
+- bump: minor
+  changes:
+    added:
+    - max_value and min_value in Variable class.

policyengine_core/variables/variable.py

@@ -132,6 +132,12 @@ class Variable:
     exhaustive_parameter_dependencies: List[str] = None
     """If these parameters (plus the dataset, branch and period) haven't changed, Core will use caching on this variable."""
 
+    min_value: (float, int) = None
+    """Minimum value of the variable."""
+
+    max_value: (float, int) = None
+    """Maximum value of the variable."""
+
     def __init__(self, baseline_variable=None):
         self.name = self.__class__.__name__
         attr = {
@@ -305,6 +311,19 @@ def __init__(self, baseline_variable=None):
                 self.exhaustive_parameter_dependencies
             ]
 
+        self.min_value = self.set(
+            attr,
+            "min_value",
+            allowed_type=(float, int),
+            setter=self.set_min_value,
+        )
+        self.max_value = self.set(
+            attr,
+            "max_value",
+            allowed_type=(float, int),
+            setter=self.set_max_value,
+        )
+
         formulas_attr, unexpected_attrs = helpers._partition(
             attr,
             lambda name, value: name.startswith(config.FORMULA_NAME_PREFIX),
@@ -463,6 +482,18 @@ def set_defined_for(self, defined_for):
             defined_for = defined_for.value
         return defined_for
 
+    def set_min_value(self, min_value):
+        if min_value is not None:
+            if self.max_value is not None and min_value > self.max_value:
+                raise ValueError("min_value cannot be greater than max_value")
+            return min_value
+
+    def set_max_value(self, max_value):
+        if max_value is not None:
+            if self.min_value is not None and max_value < self.min_value:
+                raise ValueError("max_value cannot be smaller than min_value")
+            return max_value
+
     def parse_formula_name(self, attribute_name):
         """
         Returns the starting date of a formula based on its name.

tests/core/variables/test_bounds.py

@@ -0,0 +1,79 @@
+import policyengine_core.country_template as country_template
+from policyengine_core.country_template.entities import Person
+from policyengine_core.variables import Variable
+from policyengine_core.periods import YEAR
+from test_variables import get_message
+
+tax_benefit_system = country_template.CountryTaxBenefitSystem()
+
+
+class variable__bound(Variable):
+    value_type = int
+    entity = Person
+    definition_period = YEAR
+    label = "Variable with bound."
+    min_value = 0
+    max_value = 100
+
+
+tax_benefit_system.add_variable(variable__bound)
+
+
+def test_variable__bound():
+    variable = tax_benefit_system.variables["variable__bound"]
+    assert variable.min_value == 0
+    assert variable.max_value == 100
+
+
+class variable__no_bound(Variable):
+    value_type = int
+    entity = Person
+    definition_period = YEAR
+    label = "Variable with no bound."
+
+
+tax_benefit_system.add_variable(variable__no_bound)
+
+
+def test_variable__no_bound():
+    variable = tax_benefit_system.variables["variable__no_bound"]
+    assert variable.min_value is None
+    assert variable.max_value is None
+
+
+class variable__small_max(Variable):
+    value_type = int
+    entity = Person
+    definition_period = YEAR
+    label = "Variable with max value smaller than min value."
+    min_value = 100
+    max_value = 99
+
+
+def test_variable__small_max():
+    try:
+        tax_benefit_system.add_variable(variable__small_max)
+    except ValueError as e:
+        message = get_message(e)
+        assert message.startswith("min_value cannot be greater than max_value")
+    assert not tax_benefit_system.variables.get("variable__small_max")
+
+
+class variable__wrong_type(Variable):
+    value_type = int
+    entity = Person
+    definition_period = YEAR
+    label = "Variable with wrong max value data type."
+    max_value = "string"
+
+
+def test_variable__wrong_type():
+    try:
+        tax_benefit_system.add_variable(variable__wrong_type)
+    except ValueError as e:
+        message = get_message(e)
+        assert message.startswith(
+            "Invalid value 'string' for attribute 'max_value' in variable 'variable__wrong_type'. "
+            "Must be of type '(<class 'float'>, <class 'int'>)'."
+        )
+    assert not tax_benefit_system.variables.get("variable__wrong_type")