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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _build_process_type_list(self):
 """Generates lists of processes organized by process type. Following object attributes are generated or updated: :ivar dict process_types: a dictionary with entries: ``'diagnostic'``, ``'explicit'``, ``'implicit'`` and ``'adjustment'`` which point to a list of processes according to the process types. The ``process_types`` dictionary is created while walking through the processes with :func:`~climlab.utils.walk.walk_processes` CHANGING THIS TO REFER ONLY TO THE CURRENT LEVEL IN SUBPROCESS TREE """

        self.process_types = {'diagnostic': [], 'explicit': [], 'implicit': [], 'adjustment': []}
        #for name, proc, level in walk.walk_processes(self, topdown=self.topdown):
        #    self.process_types[proc.time_type].append(proc)
        for name, proc in self.subprocess.items():
            self.process_types[proc.time_type].append(proc)
        self.has_process_type_list = True