class_docstr: Container with mappings shared across TraceTypes for placeholder values.
code: def get_placeholder(self, alias_id: Hashable) -> Hashable:
      if not self.has_placeholder(alias_id):
          raise KeyError(
              f"alias_id: {alias_id} not found in this instance of "
              "placeholder context."
          )
      return self._alias_id_to_placeholder[alias_id]
  
imports: import collections.abc
  from typing import Any, Dict, Hashable, Optional
  import weakref
  from tensorflow.core.function.trace_type import custom_nest_trace_type
  from tensorflow.core.function.trace_type import default_types
  from tensorflow.core.function.trace_type import util
  from tensorflow.python.types import trace
  from tensorflow.python.util import custom_nest_protocol
label_desc: Use image node_id 3 for calling the InternalPlaceholderContext obj's underlying member method code with example usage: obj.get_placeholder(alias_id) and returns: self