class_docstr: Dictionary with support for nans.
class_docstr_tok: ["Dictionary","with","support","for","nans","."]
code: def __init__(self, mapping):
      super().__init__(mapping)
      for key, value in mapping.items():
          if is_scalar_nan(key):
              self.nan_value = value
              break
  
file_path: mars/mars/learn/utils/_encode.py
imports: import numpy
  from typing import NamedTuple
  from ...None import tensor, dataframe
  from .core import is_scalar_nan
label_desc: Use image node_id 1 to create a new _nandict object from inherited base classes: dict with example: obj = _nandict(mapping)