code: def isnan(x, out=None, where=None, **kwargs):
      """
      Test element-wise for NaN and return result as a boolean tensor.
  
      Parameters
      ----------
      x : array_like
          Input tensor.
      out : Tensor, None, or tuple of Tensor and None, optional
          A location into which the result is stored. If provided, it must have
          a shape that the inputs broadcast to. If not provided or `None`,
          a freshly-allocated tensor is returned. A tuple (possible only as a
          keyword argument) must have length equal to the number of outputs.
      where : array_like, optional
          Values of True indicate to calculate the ufunc at that position, values
          of False indicate to leave the value in the output alone.
      **kwargs
  
      Returns
      -------
      y : Tensor or bool
          For scalar input, the result is a new boolean with value True if
          the input is NaN; otherwise the value is False.
  
          For array input, the result is a boolean tensor of the same
          dimensions as the input and the values are True if the
          corresponding element of the input is NaN; otherwise the values are
          False.
  
      See Also
      --------
      isinf, isneginf, isposinf, isfinite, isnat
  
      Notes
      -----
      Mars uses the IEEE Standard for Binary Floating-Point for Arithmetic
      (IEEE 754). This means that Not a Number is not equivalent to infinity.
  
      Examples
      --------
      >>> import mars.tensor as mt
  
      >>> mt.isnan(mt.nan).execute()
      True
      >>> mt.isnan(mt.inf).execute()
      False
      >>> mt.isnan([mt.log(-1.).execute(),1.,mt.log(0).execute()]).execute()
      array([ True, False, False])
      """
      op = TensorIsNan(**kwargs)
      return op(x, out=out, where=where)
  
file_path: mars/mars/tensor/arithmetic/isnan.py
imports: import numpy
  from ...None import opcodes
  from ..utils import inject_dtype
  from .core import TensorUnaryOp
  from .utils import arithmetic_operand
label_desc: Use image node_id 1 for calling a global function with example usage: isnan(x, out, where) and returns: op