code: def isna(obj):
      """
      Detect missing values.
  
      Return a boolean same-sized object indicating if the values are NA.
      NA values, such as None or :attr:`numpy.NaN`, gets mapped to True
      values.
  
      Everything else gets mapped to False values. Characters such as empty
      strings ``''`` or :attr:`numpy.inf` are not considered NA values
      (unless you set ``pandas.options.mode.use_inf_as_na = True``).
  
      Returns
      -------
      DataFrame
          Mask of bool values for each element in DataFrame that
          indicates whether an element is not an NA value.
  
      See Also
      --------
      DataFrame.isnull : Alias of isna.
      DataFrame.notna : Boolean inverse of isna.
      DataFrame.dropna : Omit axes labels with missing values.
      isna : Top-level isna.
  
      Examples
      --------
      Show which entries in a DataFrame are NA.
  
      >>> import numpy as np
      >>> import mars.dataframe as md
      >>> df = md.DataFrame({'age': [5, 6, np.NaN],
      ...                    'born': [md.NaT, md.Timestamp('1939-05-27'),
      ...                             md.Timestamp('1940-04-25')],
      ...                    'name': ['Alfred', 'Batman', ''],
      ...                    'toy': [None, 'Batmobile', 'Joker']})
      >>> df.execute()
         age       born    name        toy
      0  5.0        NaT  Alfred       None
      1  6.0 1939-05-27  Batman  Batmobile
      2  NaN 1940-04-25              Joker
  
      >>> df.isna().execute()
           age   born   name    toy
      0  False   True  False   True
      1  False  False  False  False
      2   True  False  False  False
  
      Show which entries in a Series are NA.
  
      >>> ser = md.Series([5, 6, np.NaN])
      >>> ser.execute()
      0    5.0
      1    6.0
      2    NaN
      dtype: float64
  
      >>> ser.isna().execute()
      0    False
      1    False
      2     True
      dtype: bool
      """
      if isinstance(obj, MultiIndex):
          raise NotImplementedError(
              "isna is not defined for MultiIndex"
          )
      elif isinstance(obj, ENTITY_TYPE):
          if isinstance(obj, TENSOR_TYPE):
              if options.dataframe.mode.use_inf_as_na:
                  return ~mt.isfinite(obj)
              else:
                  return mt.isnan(obj)
          else:
              op = DataFrameCheckNA(
                  positive=True,
                  use_inf_as_na=options.dataframe.mode.use_inf_as_na,
              )
              return op(obj)
      else:
          return _from_pandas(pd.isna(obj))
  
imports: import numpy
  import pandas
  from ...None import opcodes
  from ...None import tensor
  from ...config import options
  from ...core import OutputType
  from ...serialization.serializables import BoolField
  from ..core import MultiIndex
  from ..operands import DataFrameOperand, DataFrameOperandMixin, DATAFRAME_TYPE, ENTITY_TYPE, INDEX_TYPE, SERIES_TYPE, TENSOR_TYPE
  from typing import Any
label_desc: Use image node_id 2 for calling a global function with example usage: isna(obj) and returns: _from_pandas, op, unknown, mt