class_docstr: Mutator for changing the datatype of Relay programs.
  
  This pass should be useful for users of the Bring Your Own Datatypes
  framework.
  TODO(@gussmith23 @hypercubestart) Add link to documentation when it exists
  
  Example:
  
  .. code-block:: python
  
      from tvm.relay.testing.inception_v3 import get_workload
      mod, params = get_workload()
  
      def change_dtype(mod, params, src, dst):
          mod = ChangeDatatype(src, dst)(mod)
          params = dict((p, tvm.nd.array(params[p].numpy().astype(dst))) for p in params)
          return mod, params
  
      mod, params = change_dtype(mod, params, "float32", "custom[posites2]32")
  
  Parameters
  ----------
  src : String
      The source datatype name, e.g. "float" or "posites2" (but not "float32"
      or "custom[posites2]32").
  dst : String
      The destination datatype name, in the same format.
  
  Returns
  -------
  mod : tvm.IRModule
      Module where all nodes of dtype `src` have been changed to have dtype
      `dst`.
code: def transform_function(self, func, mod, ctx):
      return self.visit(func)
  
file_path: tvm/python/tvm/relay/frontend/change_datatype.py
imports: from ..function import Function
  from ..expr_functor import ExprMutator
  from ..transform.transform import function_pass
  from ..expr import var, bind
label_desc: Use image node_id 2 for calling the ChangeDatatype obj's underlying member method code with example usage: obj.transform_function(func, mod, ctx) and returns: self