From 6be43596cccd177d9d30e6232688c778d98cd4ae Mon Sep 17 00:00:00 2001
From: aryanputta <176622462+aryanputta@users.noreply.github.com>
Date: Fri, 26 Jun 2026 04:46:58 -0400
Subject: [PATCH] Improve Python custom validator example

---
 README.md                                     | 28 +++++++++++++++++++
 .../custom_validation.py                      | 18 +++++++++++-
 .../parameters.yaml                           |  3 +-
 3 files changed, 46 insertions(+), 3 deletions(-)

diff --git a/README.md b/README.md
index 5beb24f8..816c0319 100644
--- a/README.md
+++ b/README.md
@@ -334,6 +334,34 @@ validation:
   "my_project::integer_equal_value": [3]
 ```
 
+For Python modules, pass the validation module to `generate_parameter_module` in `setup.py`.
+The functions receive the generated `rclpy.Parameter` as the first argument and return an
+empty string when the parameter is valid. Any non-empty string is treated as the validation
+error message.
+
+```python
+generate_parameter_module(
+    module_name,
+    yaml_file,
+    validation_module='generate_parameter_module_example.custom_validation',
+)
+```
+
+The Python example includes custom validators such as:
+
+```python
+import math
+
+
+def validate_damping_ratio(param, lower_bound, upper_bound):
+    for value in param.value:
+        if not math.isfinite(value) or value <= 0.0:
+            return f"Parameter '{param.name}' must contain finite positive damping ratios"
+        if value < lower_bound or value > upper_bound:
+            return f"Value {value} in parameter '{param.name}' must be within bounds"
+    return ''
+```
+
 ### Nested structures
 After the top-level key, every subsequent non-leaf key will generate a nested C++ struct. The struct instance will have
 the same name as the key.
diff --git a/example_python/generate_parameter_module_example/custom_validation.py b/example_python/generate_parameter_module_example/custom_validation.py
index ae50ef7c..8b6a9e3d 100644
--- a/example_python/generate_parameter_module_example/custom_validation.py
+++ b/example_python/generate_parameter_module_example/custom_validation.py
@@ -26,10 +26,26 @@
 # ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 # POSSIBILITY OF SUCH DAMAGE.
 
+import math
+
 
 def no_args_validator(param):
     return ''
 
 
-def validate_double_array_custom_func(param, arg1, arg2):
+def validate_damping_ratio(param, lower_bound, upper_bound):
+    if len(param.value) != 6:
+        return f"Parameter '{param.name}' must contain six damping ratio values"
+
+    for value in param.value:
+        if not math.isfinite(value) or value <= 0.0:
+            return (
+                f"Parameter '{param.name}' must contain finite positive damping ratios"
+            )
+        if value < lower_bound or value > upper_bound:
+            return (
+                f"Value {value} in parameter '{param.name}' must be within "
+                f"[{lower_bound}, {upper_bound}]"
+            )
+
     return ''
diff --git a/example_python/generate_parameter_module_example/parameters.yaml b/example_python/generate_parameter_module_example/parameters.yaml
index 9a5d334b..fa1abb4c 100644
--- a/example_python/generate_parameter_module_example/parameters.yaml
+++ b/example_python/generate_parameter_module_example/parameters.yaml
@@ -246,8 +246,7 @@ admittance_controller:
       The values are calculated as damping can be used instead: zeta = D / (2 * sqrt( M * S ))"
       validation:
         fixed_size<>: 6
-        "custom_validators::validate_double_array_custom_func": [ 20.3, 5.0 ]
-        element_bounds<>: [ 0.1, 10.0 ]
+        "custom_validators::validate_damping_ratio": [ 0.1, 10.0 ]
 
     stiffness:
       type: double_array