========================== NumPy 1.12.0 Release Notes ========================== This release supports Python 2.7 and 3.4 - 3.6. Highlights ========== The NumPy 1.12.0 release contains a large number of fixes and improvements, but few that stand out above all others. That makes picking out the highlights somewhat arbitrary but the following may be of particular interest or indicate areas likely to have future consequences. * Order of operations in ``np.einsum`` can now be optimized for large speed improvements. * New ``signature`` argument to ``np.vectorize`` for vectorizing with core dimensions. * The ``keepdims`` argument was added to many functions. * New context manager for testing warnings * Support for BLIS in numpy.distutils * Much improved support for PyPy (not yet finished) Dropped Support =============== * Support for Python 2.6, 3.2, and 3.3 has been dropped. Added Support ============= * Support for PyPy 2.7 v5.6.0 has been added. While not complete (nditer ``updateifcopy`` is not supported yet), this is a milestone for PyPy's C-API compatibility layer. Build System Changes ==================== * Library order is preserved, instead of being reordered to match that of the directories. Deprecations ============ Assignment of ndarray object's ``data`` attribute ------------------------------------------------- Assigning the 'data' attribute is an inherently unsafe operation as pointed out in gh-7083. Such a capability will be removed in the future. Unsafe int casting of the num attribute in ``linspace`` ------------------------------------------------------- ``np.linspace`` now raises DeprecationWarning when num cannot be safely interpreted as an integer. Insufficient bit width parameter to ``binary_repr`` --------------------------------------------------- If a 'width' parameter is passed into ``binary_repr`` that is insufficient to represent the number in base 2 (positive) or 2's complement (negative) form, the function used to silently ignore the parameter and return a representation using the minimal number of bits needed for the form in question. Such behavior is now considered unsafe from a user perspective and will raise an error in the future. Future Changes ============== * In 1.13 NAT will always compare False except for ``NAT != NAT``, which will be True. In short, NAT will behave like NaN * In 1.13 ``np.average`` will preserve subclasses, to match the behavior of most other numpy functions such as np.mean. In particular, this means calls which returned a scalar may return a 0-d subclass object instead. Multiple-field manipulation of structured arrays ------------------------------------------------ In 1.13 the behavior of structured arrays involving multiple fields will change in two ways: First, indexing a structured array with multiple fields (eg, ``arr[['f1', 'f3']]``) will return a view into the original array in 1.13, instead of a copy. Note the returned view will have extra padding bytes corresponding to intervening fields in the original array, unlike the copy in 1.12, which will affect code such as ``arr[['f1', 'f3']].view(newdtype)``. Second, for numpy versions 1.6 to 1.12 assignment between structured arrays occurs "by field name": Fields in the destination array are set to the identically-named field in the source array or to 0 if the source does not have a field:: >>> a = np.array([(1,2),(3,4)], dtype=[('x', 'i4'), ('y', 'i4')]) >>> b = np.ones(2, dtype=[('z', 'i4'), ('y', 'i4'), ('x', 'i4')]) >>> b[:] = a >>> b array([(0, 2, 1), (0, 4, 3)], dtype=[('z', '`. This allows for vectorizing a much broader class of functions. For example, an arbitrary distance metric that combines two vectors to produce a scalar could be vectorized with ``signature='(n),(n)->()'``. See ``np.vectorize`` for full details. Emit py3kwarnings for division of integer arrays ------------------------------------------------ To help people migrate their code bases from Python 2 to Python 3, the python interpreter has a handy option -3, which issues warnings at runtime. One of its warnings is for integer division:: $ python -3 -c "2/3" -c:1: DeprecationWarning: classic int division In Python 3, the new integer division semantics also apply to numpy arrays. With this version, numpy will emit a similar warning:: $ python -3 -c "import numpy as np; np.array(2)/np.array(3)" -c:1: DeprecationWarning: numpy: classic int division numpy.sctypes now includes bytes on Python3 too ----------------------------------------------- Previously, it included str (bytes) and unicode on Python2, but only str (unicode) on Python3. Improvements ============ ``bitwise_and`` identity changed -------------------------------- The previous identity was 1 with the result that all bits except the LSB were masked out when the reduce method was used. The new identity is -1, which should work properly on twos complement machines as all bits will be set to one. Generalized Ufuncs will now unlock the GIL ------------------------------------------ Generalized Ufuncs, including most of the linalg module, will now unlock the Python global interpreter lock. Caches in `np.fft` are now bounded in total size and item count --------------------------------------------------------------- The caches in `np.fft` that speed up successive FFTs of the same length can no longer grow without bounds. They have been replaced with LRU (least recently used) caches that automatically evict no longer needed items if either the memory size or item count limit has been reached. Improved handling of zero-width string/unicode dtypes ----------------------------------------------------- Fixed several interfaces that explicitly disallowed arrays with zero-width string dtypes (i.e. ``dtype('S0')`` or ``dtype('U0')``, and fixed several bugs where such dtypes were not handled properly. In particular, changed ``ndarray.__new__`` to not implicitly convert ``dtype('S0')`` to ``dtype('S1')`` (and likewise for unicode) when creating new arrays. Integer ufuncs vectorized with AVX2 ----------------------------------- If the cpu supports it at runtime the basic integer ufuncs now use AVX2 instructions. This feature is currently only available when compiled with GCC. Order of operations optimization in ``np.einsum`` -------------------------------------------------- ``np.einsum`` now supports the ``optimize`` argument which will optimize the order of contraction. For example, ``np.einsum`` would complete the chain dot example ``np.einsum(‘ij,jk,kl->il’, a, b, c)`` in a single pass which would scale like ``N^4``; however, when ``optimize=True`` ``np.einsum`` will create an intermediate array to reduce this scaling to ``N^3`` or effectively ``np.dot(a, b).dot(c)``. Usage of intermediate tensors to reduce scaling has been applied to the general einsum summation notation. See ``np.einsum_path`` for more details. quicksort has been changed to an introsort ------------------------------------------ The quicksort kind of ``np.sort`` and ``np.argsort`` is now an introsort which is regular quicksort but changing to a heapsort when not enough progress is made. This retains the good quicksort performance while changing the worst case runtime from ``O(N^2)`` to ``O(N*log(N))``. ``ediff1d`` improved performance and subclass handling ------------------------------------------------------ The ediff1d function uses an array instead on a flat iterator for the subtraction. When to_begin or to_end is not None, the subtraction is performed in place to eliminate a copy operation. A side effect is that certain subclasses are handled better, namely astropy.Quantity, since the complete array is created, wrapped, and then begin and end values are set, instead of using concatenate. Improved precision of ``ndarray.mean`` for float16 arrays --------------------------------------------------------- The computation of the mean of float16 arrays is now carried out in float32 for improved precision. This should be useful in packages such as Theano where the precision of float16 is adequate and its smaller footprint is desirable. Changes ======= All array-like methods are now called with keyword arguments in fromnumeric.py ------------------------------------------------------------------------------ Internally, many array-like methods in fromnumeric.py were being called with positional arguments instead of keyword arguments as their external signatures were doing. This caused a complication in the downstream 'pandas' library that encountered an issue with 'numpy' compatibility. Now, all array-like methods in this module are called with keyword arguments instead. Operations on np.memmap objects return numpy arrays in most cases ----------------------------------------------------------------- Previously operations on a memmap object would misleadingly return a memmap instance even if the result was actually not memmapped. For example, ``arr + 1`` or ``arr + arr`` would return memmap instances, although no memory from the output array is memmapped. Version 1.12 returns ordinary numpy arrays from these operations. Also, reduction of a memmap (e.g. ``.sum(axis=None``) now returns a numpy scalar instead of a 0d memmap. stacklevel of warnings increased -------------------------------- The stacklevel for python based warnings was increased so that most warnings will report the offending line of the user code instead of the line the warning itself is given. Passing of stacklevel is now tested to ensure that new warnings will receive the ``stacklevel`` argument. This causes warnings with the "default" or "module" filter to be shown once for every offending user code line or user module instead of only once. On python versions before 3.4, this can cause warnings to appear that were falsely ignored before, which may be surprising especially in test suits.