Recent versions of PyYAML break dynamic_reconfigure_load

There seems to be recent API changes in PyYAML (either starting at 5.3.1 or 5.4) which will cause dynamic_reconfigure_load to crash on Ubuntu 20.04 with ROS noetic.

Given this example dynamic_reconfigure setup:

#!/usr/bin/env python

# set ROS package name
PACKAGE = "my_package"

from dynamic_reconfigure.parameter_generator_catkin import *

gen = ParameterGenerator()

# define parameters
gen.add("parameter_float",  double_t,   0,  "floating point number parameter",  0.5, 0.0, 1.0)
gen.add("parameter_bool",   bool_t,     0,  "boolean parameter",                True)
gen.add("parameter_string", str_t,      0,  "string parameter",                 "Hello World!")

nodeNameForDocumentation = "my_node"
thisConfigFile = os.path.splitext(os.path.basename(__file__))[0] # the generated header will be prefixed by this file's name (<thisConfigFile>Config.h)
exit(gen.generate(PACKAGE, nodeNameForDocumentation, thisConfigFile))

and an input config.yaml file exported by rqt_reconfigure:

!!python/object/new:dynamic_reconfigure.encoding.Config
dictitems:
  groups: !!python/object/new:dynamic_reconfigure.encoding.Config
    dictitems:
      groups: !!python/object/new:dynamic_reconfigure.encoding.Config
        state: []
      id: 0
      name: Default
      parameter_bool: false
      parameter_float: 0.75
      parameter_string: Hello World!
      parameters: !!python/object/new:dynamic_reconfigure.encoding.Config
        state: []
      parent: 0
      state: true
      type: ''
    state: []
  parameter_bool: false
  parameter_float: 0.75
  parameter_string: Hello World!
state: []

Loading in this file from a .launch file:

<launch>
  <group ns="/my_package">
    <node pkg="my_package" type="my_node" name="my_node"/>
  </group>
  <node name="dynamic_reconfigure_load" pkg="dynamic_reconfigure" type="dynparam" args="load /my_package/my_node $(find my_package)/config.yaml" />
</launch>

Results in the following crash:

Traceback (most recent call last):
  File "/opt/ros/noetic/lib/dynamic_reconfigure/dynparam", line 240, in <module>
    elif cmd == 'load':                do_load()
  File "/opt/ros/noetic/lib/dynamic_reconfigure/dynparam", line 162, in do_load
    for doc in yaml.load_all(f.read()):
  File "/home/rosuser/.local/lib/python3.8/site-packages/yaml/__init__.py", line 130, in load_all
    yield loader.get_data()
  File "/home/rosuser/.local/lib/python3.8/site-packages/yaml/constructor.py", line 45, in get_data
    return self.construct_document(self.get_node())
  File "/home/rosuser/.local/lib/python3.8/site-packages/yaml/constructor.py", line 55, in construct_document
    data = self.construct_object(node)
  File "/home/rosuser/.local/lib/python3.8/site-packages/yaml/constructor.py", line 100, in construct_object
    data = constructor(self, node)
  File "/home/rosuser/.local/lib/python3.8/site-packages/yaml/constructor.py", line 427, in construct_undefined
    raise ConstructorError(None, None,
yaml.constructor.ConstructorError: could not determine a constructor for the tag 'tag:yaml.org,2002:python/object/new:dynamic_reconfigure.encoding.Config'
  in "<unicode string>", line 1, column 1:
    !!python/object/new:dynamic_reco ... 
    ^
[my_package/dynamic_reconfigure_load-2] process has died [pid 1185, exit code 1, cmd /opt/ros/noetic/lib/dynamic_reconfigure/dynparam load /my_package/my_node /home/rosuser/my_package/config.yaml __name:=dynamic_reconfigure_load __log:=/home/rosuser/.ros/log/12a48208-d583-11eb-a63e-0242d5aa77ae/my_package-dynamic_reconfigure_load-2.log].
log file: /home/rosuser/.ros/log/12a48208-d583-11eb-a63e-0242d5aa77ae/my_package-dynamic_reconfigure_load-2*.log

pip list outputs:

PyYAML                        5.3.1

Updating to 5.4 shows the same behaviour.

Downgrading to 5.3 however using

pip install PyYAML==5.3

fixes the crash and the parameters are loaded in correctly. Interestingly, upgrading from 5.3 to 5.3.1 appears to be safe (i.e. no crash) - so I'm not entirely sure if its 5.3.1 or 5.4 which introduces the incompatibility.

ros / dynamic_reconfigure

Recent versions of PyYAML break dynamic_reconfigure_load #179