ROS2-2001 ros2 config_error ai_generated true

ros2 launch: Substitution error: parameter 'my_param' expected type 'double' but got 'integer'

ID: ros2/ros2-launch-parameter-substitution-type-mismatch

Also available as: JSON · Markdown · 中文

90%Fix Rate

85%Confidence

1Evidence

2024-01-10First Seen

Version Compatibility

Version	Status	Introduced	Deprecated	Notes
ros2:humble	active	—	—	—
ros2:iron	active	—	—	—
ros2:rolling	active	—	—	—
launch:2.0.0	active	—	—	—

Root Cause

Launch file uses a substitution that evaluates to a type incompatible with the declared parameter type (e.g., integer vs double) due to LaunchConfiguration or Python substitution returning an int instead of float.

generic

中文

启动文件使用的替换结果与声明的参数类型不兼容（例如整数 vs 双精度浮点数），因为 LaunchConfiguration 或 Python 替换返回了 int 而非 float。

Official Documentation

https://docs.ros.org/en/humble/Tutorials/Intermediate/Launch/Using-Substitutions.html

Workarounds

90% success Explicitly cast the substitution to the expected type using PythonExpression. Example: from launch.substitutions import PythonExpression param_value = PythonExpression(['float(', LaunchConfiguration('my_param'), ')']) This forces the substitution to evaluate to a float.
```
Explicitly cast the substitution to the expected type using PythonExpression. Example:
from launch.substitutions import PythonExpression

param_value = PythonExpression(['float(', LaunchConfiguration('my_param'), ')'])

This forces the substitution to evaluate to a float.
```
85% success In the launch file, use a typed substitution like FloatSubstitution if available, or ensure the LaunchConfiguration default is a float: from launch.substitutions import LaunchConfiguration param = LaunchConfiguration('my_param', default=0.0) # default as float
```
In the launch file, use a typed substitution like FloatSubstitution if available, or ensure the LaunchConfiguration default is a float:
from launch.substitutions import LaunchConfiguration

param = LaunchConfiguration('my_param', default=0.0)  # default as float
```

中文步骤

使用 PythonExpression 显式将替换结果转换为期望类型。示例：
from launch.substitutions import PythonExpression

param_value = PythonExpression(['float(', LaunchConfiguration('my_param'), ')'])

这将强制替换结果为浮点数。

在启动文件中使用类型化替换（如 FloatSubstitution，如果可用），或确保 LaunchConfiguration 默认值为浮点数：
from launch.substitutions import LaunchConfiguration

param = LaunchConfiguration('my_param', default=0.0)  # 默认值为浮点数

Dead Ends

Common approaches that don't work:

Changing the parameter type in the node's declaration to match the substitution type 50% fail
The node may expect a specific type for correct operation; changing the declaration can cause runtime errors in the node.
Wrapping the substitution in str() without converting to the correct numeric type 90% fail
String substitution will be interpreted as a string, not a number, causing a different type mismatch error.