polars.Series.to_numpy#

Series.to_numpy(
*,
writable: bool = False,
allow_copy: bool = True,
use_pyarrow: bool | None = None,
zero_copy_only: bool | None = None,
) → ndarray[Any, Any][source]#

Convert this Series to a NumPy ndarray.

This operation copies data only when necessary. The conversion is zero copy when all of the following hold:

  • The data type is an integer, float, Datetime, Duration, or Array.

  • The Series contains no null values.

  • The Series consists of a single chunk.

  • The writable parameter is set to False (default).

Parameters:
writable

Ensure the resulting array is writable. This will force a copy of the data if the array was created without copy as the underlying Arrow data is immutable.

allow_copy

Allow memory to be copied to perform the conversion. If set to False, causes conversions that are not zero-copy to fail.

use_pyarrow

First convert to PyArrow, then call pyarrow.Array.to_numpy to convert to NumPy. If set to False, Polars’ own conversion logic is used.

Deprecated since version 0.20.28: Polars now uses its native engine by default for conversion to NumPy. To use PyArrow’s engine, call .to_arrow().to_numpy() instead.

zero_copy_only

Raise an exception if the conversion to a NumPy would require copying the underlying data. Data copy occurs, for example, when the Series contains nulls or non-numeric types.

Deprecated since version 0.20.10: Use the allow_copy parameter instead, which is the inverse of this one.

Examples

Numeric data without nulls can be converted without copying data. The resulting array will not be writable.

>>> s = pl.Series([1, 2, 3], dtype=pl.Int8)
>>> arr = s.to_numpy()
>>> arr
array([1, 2, 3], dtype=int8)
>>> arr.flags.writeable
False

Set writable=True to force data copy to make the array writable.

>>> s.to_numpy(writable=True).flags.writeable
True

Integer Series containing nulls will be cast to a float type with nan representing a null value. This requires data to be copied.

>>> s = pl.Series([1, 2, None], dtype=pl.UInt16)
>>> s.to_numpy()
array([ 1.,  2., nan], dtype=float32)

Set allow_copy=False to raise an error if data would be copied.

>>> s.to_numpy(allow_copy=False)  
Traceback (most recent call last):
...
RuntimeError: copy not allowed: cannot convert to a NumPy array without copying data

Series of data type Array and Struct will result in an array with more than one dimension.

>>> s = pl.Series([[1, 2, 3], [4, 5, 6]], dtype=pl.Array(pl.Int64, 3))
>>> s.to_numpy()
array([[1, 2, 3],
       [4, 5, 6]])
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