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numpy.isnan() in Python
• Last Updated : 23 Oct, 2020

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 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 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 wonβt run on online-ID. Please run them on your systems to explore the working.
.
This article is contributed by Mohit Gupta_OMG π. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.