cannot index into python dict or Mapping with subsasgn

a = py.dict(pyargs('key','value'))

a{'key'} = 'value2'

error: invalid dot name structure assignment because the structure array is empty. Specify a subscript on the structure array to resolve

This method of assigning to the python dictionary produces an error. There may be other methods to perform the task, but the presence of this method will help maintain uniformity with other python types like list which can be assigned as a{1} = xx. Matlab also has this type of assignment option.