class_docstr: An operator stream that accumulates values of a given stream.
  
  Parameters
  ----------
  func : Callable[[T,T], T]
      An accumulator function.
  dtype : str
      The data type of accumulated value.
class_docstr_tok: ["An","operator","stream","that","accumulates","values","of","a","given","stream",".","Parameters","--","--","--","--","--","func",":","Callable","[","[","T",",","T","]",",","T","]","An","accumulator","function",".","dtype",":","str","The","data","type","of","accumulated","value","."]
code: def forward(self):
      node = self.inputs[0]
      if self.past is None:
          self.past = node.value
          return self.past
      v = self.func(self.past, node.value)
      self.past = v
      return v
  
imports: from typing import Callable, TypeVar
  import numpy
  from tensortrade.feed.core.base import Stream, T
label_desc: Use image node_id 2 for calling the Accumulator obj's underlying member method code with example usage: obj.forward() and returns: v, self