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# numpy.isnan() in Python

The numpy.isnan() function tests element-wise whether it is NaN or not and returns the result as a boolean array. Syntax :

`numpy.isnan(array [, out])`

Parameters :

```array : [array_like]Input array or object whose elements, we need to test for infinity
out   : [ndarray, optional]Output array placed with result.
Its type is preserved and it must be of the right shape to hold the output.```

Return :

```boolean array containing the result. For scalar input, the result is a new boolean with value
True if the input is positive or negative infinity; otherwise the value is False.
For array input, the result is a boolean array with the same shape as the input and the values
are True where the corresponding element of the input is positive or negative infinity;
elsewhere the values are False.```

Code 1 :

## Python

 `# Python Program illustrating``# numpy.isnan() method`` ` `import` `numpy as geek` `print``("Is NaN : ", geek.isnan(``1``), "\n")` `print``("Is NaN : ", geek.isnan(``0``), "\n")` `# not a number``print``("Is NaN : ", geek.isnan(geek.nan), "\n")` `#  infinity``print``("Is NaN : ", geek.isnan(geek.inf), "\n")` `print``("Is NaN : ", geek.isnan(geek.NINF), "\n")` `x ``=` `geek.array([``-``geek.inf, ``0.``, geek.inf])``y ``=` `geek.array([``2``, ``2``, ``2``])``print``("Checking ``for` `NaN : ", geek.isnan(x, y))`

Output :

```Is NaN :  False

Is NaN :  False

Is NaN :  True

Is NaN :  False

Is NaN :  False

Checking for NaN :  [0 0 0]```

Code 2 :

## Python

 `# Python Program illustrating``# numpy.isnan() method``  ` `import` `numpy as geek`` ` `# Returns True/False value for each element``b ``=` `geek.arange(``20``).reshape(``5``, ``4``)``               ` `print``("\n",b)``print``("\nIs NaN(Not a Number): \n", geek.isnan(b))`  `b ``=` `[[``1j``],``     ``[geek.nan]]``print``("\nIs NaN(Not a Number) : \n", geek.isnan(b))`

Output :

``` [[ 0  1  2  3]
[ 4  5  6  7]
[ 8  9 10 11]
[12 13 14 15]
[16 17 18 19]]

Is NaN(Not a Number):
[[False False False False]
[False False False False]
[False False False False]
[False False False False]
[False False False False]]

Is NaN(Not a Number) :
[[False]
[ True]]```

Note : These codes won’t run on online IDE’s. So please, run them on your systems to explore the working.