parameter_dict_from_yaml_file loads doubles as strings when str() uses exponent notation (e.g. 0.00001, 5e-06, 1e+20)

[Lots-ninety-nine]

Bug report

Required Info:

• Operating System: Ubuntu 24.04 (osrf/ros:rolling-desktop)
• Installation type: binaries
• Version or commit hash: rolling (the offending line is still present on the rolling branch, rclpy/parameter.py:565)
• DDS implementation: rmw_fastrtps_cpp
• Client library (if applicable): rclpy

Description

parameter_dict_from_yaml_file (used by ros2 param load) loads floating-point parameters as strings whenever the value's Python str() representation uses exponent notation, e.g. 0.00001, 5e-06, 1.0e+20. Plain decimals such as 3.14 are unaffected. This also affects double arrays.

Steps to reproduce issue

repro.yaml:

/parameter_blackboard:
  ros__parameters:
    a_small: 0.00001
    b_sci: 5e-06
    c_large: 1.0e+20
    d_normal: 3.14
    e_arr: [1.0e-5, 2.0e-5]

ros2 run demo_nodes_cpp parameter_blackboard &
ros2 param load /parameter_blackboard repro.yaml
for p in a_small b_sci c_large d_normal e_arr; do ros2 param get /parameter_blackboard $p; done

Expected behavior

a_small, b_sci, c_large are doubles and e_arr is a double array — matching what the C++ params-file loader (--params-file) and ros2 param set already produce for the same values.

Actual behavior

a_small   -> String value is: 1e-05
b_sci     -> String value is: 5e-06
c_large   -> String value is: 1e+20
d_normal  -> Double value is: 3.14
e_arr     -> String values are: ['1e-05', '2e-05']

Root cause

In _unpack_parameter_dict (rclpy/parameter.py):

parameter.value = get_parameter_value(str(param_value))

yaml.safe_load parses the file and already types these values correctly as floats. _unpack_parameter_dict then converts each value back to a string with str() and re-parses it through get_parameter_value → yaml.safe_load. For magnitudes where str(float) yields exponent notation without a decimal point (1e-05, 5e-06, 1e+20), PyYAML's YAML 1.1 implicit resolver does not treat the result as a float (it requires a .), so it returns a str and the parameter is created with type STRING.

The float → str() → YAML round-trip discards the type that yaml.safe_load already determined. Building the ParameterValue from the already-parsed Python value, instead of re-parsing str(param_value), avoids the lossy round-trip.

This is the same underlying problem reported in ros2/ros2cli#834, but the fix is local to rclpy. Happy to open a PR.

[fujitatomoya]

@Barry-Xu-2018 can you take a look at this when you can allocate time?

[Barry-Xu-2018]

This issue is a known problem. The reason is that PyYAML only supports YAML 1.1. The enhancement request at yaml/pyyaml#174 has also been closed. Support for YAML 1.2 in PyYAML is under consideration, but it has not been implemented so far.

Would you like to consider using a workaround to solve this in rclpy?