NumPy 1.23.0 Release Notes#

The NumPy 1.23.0 release continues the ongoing work to improve the handling and promotion of dtypes, increase the execution speed, clarify the documentation, and expire old deprecations. The highlights are:

  • Implementation of loadtxt in C, greatly improving its performance.

  • Exposing DLPack at the Python level for easy data exchange.

  • Changes to the promotion and comparisons of structured dtypes.

  • Improvements to f2py.

See below for the details,

New functions#

  • A masked array specialization of ndenumerate is now available as numpy.ma.ndenumerate. It provides an alternative to numpy.ndenumerate and skips masked values by default.

    (gh-20020)

  • numpy.from_dlpack has been added to allow easy exchange of data using the DLPack protocol. It accepts Python objects that implement the __dlpack__ and __dlpack_device__ methods and returns a ndarray object which is generally the view of the data of the input object.

    (gh-21145)

Deprecations#

  • Setting __array_finalize__ to None is deprecated. It must now be a method and may wish to call super().__array_finalize__(obj) after checking for None or if the NumPy version is sufficiently new.

    (gh-20766)

  • Using axis=32 (axis=np.MAXDIMS) in many cases had the same meaning as axis=None. This is deprecated and axis=None must be used instead.

    (gh-20920)

  • The hook function PyDataMem_SetEventHook has been deprecated and the demonstration of its use in tool/allocation_tracking has been removed. The ability to track allocations is now built-in to python via tracemalloc.

    (gh-20394)

  • numpy.distutils has been deprecated, as a result of distutils itself being deprecated. It will not be present in NumPy for Python >= 3.12, and will be removed completely 2 years after the release of Python 3.12 For more details, see Status of numpy.distutils and migration advice.

    (gh-20875)

  • numpy.loadtxt will now give a DeprecationWarning when an integer dtype is requested but the value is formatted as a floating point number.

    (gh-21663)

Expired deprecations#

  • The NpzFile.iteritems() and NpzFile.iterkeys() methods have been removed as part of the continued removal of Python 2 compatibility. This concludes the deprecation from 1.15.

    (gh-16830)

  • The alen and asscalar functions have been removed.

    (gh-20414)

  • The UPDATEIFCOPY array flag has been removed together with the enum NPY_ARRAY_UPDATEIFCOPY. The associated (and deprecated) PyArray_XDECREF_ERR was also removed. These were all deprecated in 1.14. They are replaced by NPY_ARRAY_WRITEBACKIFCOPY, that requires calling PyArray_ResolveWritebackIfCopy before the array is deallocated.

    (gh-20589)

  • Exceptions will be raised during array-like creation. When an object raised an exception during access of the special attributes __array__ or __array_interface__, this exception was usually ignored. This behaviour was deprecated in 1.21, and the exception will now be raised.

    (gh-20835)

  • Multidimensional indexing with non-tuple values is not allowed. Previously, code such as arr[ind] where ind = [[0, 1], [0, 1]] produced a FutureWarning and was interpreted as a multidimensional index (i.e., arr[tuple(ind)]). Now this example is treated like an array index over a single dimension (arr[array(ind)]). Multidimensional indexing with anything but a tuple was deprecated in NumPy 1.15.

    (gh-21029)

  • Changing to a dtype of different size in F-contiguous arrays is no longer permitted. Deprecated since Numpy 1.11.0. See below for an extended explanation of the effects of this change.

    (gh-20722)

New Features#

crackfortran has support for operator and assignment overloading#

crackfortran parser now understands operator and assignment definitions in a module. They are added in the body list of the module which contains a new key implementedby listing the names of the subroutines or functions implementing the operator or assignment.

(gh-15006)

f2py supports reading access type attributes from derived type statements#

As a result, one does not need to use public or private statements to specify derived type access properties.

(gh-15844)

New parameter ndmin added to genfromtxt#

This parameter behaves the same as ndmin from numpy.loadtxt.

(gh-20500)

np.loadtxt now supports quote character and single converter function#

numpy.loadtxt now supports an additional quotechar keyword argument which is not set by default. Using quotechar='"' will read quoted fields as used by the Excel CSV dialect.

Further, it is now possible to pass a single callable rather than a dictionary for the converters argument.

(gh-20580)

Changing to dtype of a different size now requires contiguity of only the last axis#

Previously, viewing an array with a dtype of a different item size required that the entire array be C-contiguous. This limitation would unnecessarily force the user to make contiguous copies of non-contiguous arrays before being able to change the dtype.

This change affects not only ndarray.view, but other construction mechanisms, including the discouraged direct assignment to ndarray.dtype.

This change expires the deprecation regarding the viewing of F-contiguous arrays, described elsewhere in the release notes.

(gh-20722)

Deterministic output files for F2PY#

For F77 inputs, f2py will generate modname-f2pywrappers.f unconditionally, though these may be empty. For free-form inputs, modname-f2pywrappers.f, modname-f2pywrappers2.f90 will both be generated unconditionally, and may be empty. This allows writing generic output rules in cmake or meson and other build systems. Older behavior can be restored by passing --skip-empty-wrappers to f2py. Using via meson details usage.

(gh-21187)

keepdims parameter for average#

The parameter keepdims was added to the functions numpy.average and numpy.ma.average. The parameter has the same meaning as it does in reduction functions such as numpy.sum or numpy.mean.

(gh-21485)

New parameter equal_nan added to np.unique#

np.unique was changed in 1.21 to treat all NaN values as equal and return a single NaN. Setting equal_nan=False will restore pre-1.21 behavior to treat NaNs as unique. Defaults to True.

(gh-21623)

Compatibility notes#

1D np.linalg.norm preserves float input types, even for scalar results#

Previously, this would promote to float64 when the ord argument was not one of the explicitly listed values, e.g. ord=3:

>>> f32 = np.float32([1, 2])
>>> np.linalg.norm(f32, 2).dtype
dtype('float32')
>>> np.linalg.norm(f32, 3)
dtype('float64')  # numpy 1.22
dtype('float32')  # numpy 1.23

This change affects only float32 and float16 vectors with ord other than -Inf, 0, 1, 2, and Inf.

(gh-17709)

Changes to structured (void) dtype promotion and comparisons#

In general, NumPy now defines correct, but slightly limited, promotion for structured dtypes by promoting the subtypes of each field instead of raising an exception:

>>> np.result_type(np.dtype("i,i"), np.dtype("i,d"))
dtype([('f0', '<i4'), ('f1', '<f8')])

For promotion matching field names, order, and titles are enforced, however padding is ignored. Promotion involving structured dtypes now always ensures native byte-order for all fields (which may change the result of np.concatenate) and ensures that the result will be “packed”, i.e. all fields are ordered contiguously and padding is removed. See Structure comparison and promotion for further details.

The repr of aligned structures will now never print the long form including offsets and itemsize unless the structure includes padding not guaranteed by align=True.

In alignment with the above changes to the promotion logic, the casting safety has been updated:

  • "equiv" enforces matching names and titles. The itemsize is allowed to differ due to padding.

  • "safe" allows mismatching field names and titles

  • The cast safety is limited by the cast safety of each included field.

  • The order of fields is used to decide cast safety of each individual field. Previously, the field names were used and only unsafe casts were possible when names mismatched.

The main important change here is that name mismatches are now considered “safe” casts.

(gh-19226)

NPY_RELAXED_STRIDES_CHECKING has been removed#

NumPy cannot be compiled with NPY_RELAXED_STRIDES_CHECKING=0 anymore. Relaxed strides have been the default for many years and the option was initially introduced to allow a smoother transition.

(gh-20220)

np.loadtxt has received several changes#

The row counting of numpy.loadtxt was fixed. loadtxt ignores fully empty lines in the file, but counted them towards max_rows. When max_rows is used and the file contains empty lines, these will now not be counted. Previously, it was possible that the result contained fewer than max_rows rows even though more data was available to be read. If the old behaviour is required, itertools.islice may be used:

import itertools
lines = itertools.islice(open("file"), 0, max_rows)
result = np.loadtxt(lines, ...)

While generally much faster and improved, numpy.loadtxt may now fail to converter certain strings to numbers that were previously successfully read. The most important cases for this are:

  • Parsing floating point values such as 1.0 into integers is now deprecated.

  • Parsing hexadecimal floats such as 0x3p3 will fail

  • An _ was previously accepted as a thousands delimiter 100_000. This will now result in an error.

If you experience these limitations, they can all be worked around by passing appropriate converters=. NumPy now supports passing a single converter to be used for all columns to make this more convenient. For example, converters=float.fromhex can read hexadecimal float numbers and converters=int will be able to read 100_000.

Further, the error messages have been generally improved. However, this means that error types may differ. In particularly, a ValueError is now always raised when parsing of a single entry fails.

(gh-20580)

Improvements#

ndarray.__array_finalize__ is now callable#

This means subclasses can now use super().__array_finalize__(obj) without worrying whether ndarray is their superclass or not. The actual call remains a no-op.

(gh-20766)

Add support for VSX4/Power10#

With VSX4/Power10 enablement, the new instructions available in Power ISA 3.1 can be used to accelerate some NumPy operations, e.g., floor_divide, modulo, etc.

(gh-20821)

np.fromiter now accepts objects and subarrays#

The numpy.fromiter function now supports object and subarray dtypes. Please see he function documentation for examples.

(gh-20993)

Math C library feature detection now uses correct signatures#

Compiling is preceded by a detection phase to determine whether the underlying libc supports certain math operations. Previously this code did not respect the proper signatures. Fixing this enables compilation for the wasm-ld backend (compilation for web assembly) and reduces the number of warnings.

(gh-21154)

np.kron now maintains subclass information#

np.kron maintains subclass information now such as masked arrays while computing the Kronecker product of the inputs

>>> x = ma.array([[1, 2], [3, 4]], mask=[[0, 1], [1, 0]])
>>> np.kron(x,x)
masked_array(
  data=[[1, --, --, --],
        [--, 4, --, --],
        [--, --, 4, --],
        [--, --, --, 16]],
  mask=[[False,  True,  True,  True],
        [ True, False,  True,  True],
        [ True,  True, False,  True],
        [ True,  True,  True, False]],
  fill_value=999999)

Warning

np.kron output now follows ufunc ordering (multiply) to determine the output class type

>>> class myarr(np.ndarray):
>>>    __array_priority__ = -1
>>> a = np.ones([2, 2])
>>> ma = myarray(a.shape, a.dtype, a.data)
>>> type(np.kron(a, ma)) == np.ndarray
False # Before it was True
>>> type(np.kron(a, ma)) == myarr
True

(gh-21262)

Performance improvements and changes#

Faster np.loadtxt#

numpy.loadtxt is now generally much faster than previously as most of it is now implemented in C.

(gh-20580)

Faster reduction operators#

Reduction operations like numpy.sum, numpy.prod, numpy.add.reduce, numpy.logical_and.reduce on contiguous integer-based arrays are now much faster.

(gh-21001)

Faster np.where#

numpy.where is now much faster than previously on unpredictable/random input data.

(gh-21130)

Faster operations on NumPy scalars#

Many operations on NumPy scalars are now significantly faster, although rare operations (e.g. with 0-D arrays rather than scalars) may be slower in some cases. However, even with these improvements users who want the best performance for their scalars, may want to convert a known NumPy scalar into a Python one using scalar.item().

(gh-21188)

Faster np.kron#

numpy.kron is about 80% faster as the product is now computed using broadcasting.

(gh-21354)