The class inspect.Signature asks for parameters of type dict in python 3.8+ (and OrderedDict in earlier versions); however the __init__ function iterates over parameters as if it were a list, specifically:

for param in parameters:
    name = param.name
    kind = param.kind
    ...

Either the docstring should be changed to specify Sequence / List, or the implementation should be changed to iterate over the values of parameters:

for param in parameters.values():
    ...

(https://github.com/python/cpython/blob/2cca8efe46935c39c445f585bce54954fad2485b/Lib/inspect.py#L2734)