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  * polars.Expr.... 

#  polars.Expr.rolling_std  #

Expr.  rolling_std  (

     _ window_size  :  [ int  ](https://docs.python.org/3/library/functions.html#int "\(in Python v3.12\)") |  timedelta  |  [ str  ](https://docs.python.org/3/library/stdtypes.html#str "\(in Python v3.12\)") _ , 
     _ weights  :  [ list  ](https://docs.python.org/3/library/stdtypes.html#list "\(in Python v3.12\)") [  [ float  ](https://docs.python.org/3/library/functions.html#float "\(in Python v3.12\)") ]  |  [ None  ](https://docs.python.org/3/library/constants.html#None "\(in Python v3.12\)") =  None  _ , 
     _ min_periods  :  [ int  ](https://docs.python.org/3/library/functions.html#int "\(in Python v3.12\)") |  [ None  ](https://docs.python.org/3/library/constants.html#None "\(in Python v3.12\)") =  None  _ , 
     _ *  _ , 
     _ center  :  [ bool  ](https://docs.python.org/3/library/functions.html#bool "\(in Python v3.12\)") =  False  _ , 
     _ by  :  [ str  ](https://docs.python.org/3/library/stdtypes.html#str "\(in Python v3.12\)") |  [ None  ](https://docs.python.org/3/library/constants.html#None "\(in Python v3.12\)") =  None  _ , 
     _ closed  :  ClosedInterval  |  [ None  ](https://docs.python.org/3/library/constants.html#None "\(in Python v3.12\)") =  None  _ , 
     _ ddof  :  [ int  ](https://docs.python.org/3/library/functions.html#int "\(in Python v3.12\)") =  1  _ , 
     _ warn_if_unsorted  :  [ bool  ](https://docs.python.org/3/library/functions.html#bool "\(in Python v3.12\)") =  True  _ , 
)  →  Self  [ [source]  ](https://github.com/pola-rs/polars/blob/main/py-
polars/polars/expr/expr.py#L6996-L7242) #

    

Compute a rolling standard deviation.

Warning

This functionality is considered **unstable** . It may be changed at any point
without it being considered a breaking change.

If ` by  ` has not been specified (the default), the window at a given row
will include the row itself, and the ` window_size  -  1  ` elements before
it.

If you pass a ` by  ` column ` <t_0,  t_1,  ...,  t_n> ` , then `
closed="left"  ` means the windows will be:

>   * [t_0 - window_size, t_0)
>
>   * [t_1 - window_size, t_1)
>
>   * …
>
>   * [t_n - window_size, t_n)
>
>

Parameters  :

    

**window_size**

    

The length of the window. Can be a fixed integer size, or a dynamic temporal
size indicated by a timedelta or the following string language:

  * 1ns (1 nanosecond) 

  * 1us (1 microsecond) 

  * 1ms (1 millisecond)