Function fuse_slice

dask/array/optimization.py:222–318

Fuse stacked slices together Fuse a pair of repeated slices into a single slice: >>> fuse_slice(slice(1000, 2000), slice(10, 15)) slice(1010, 1015, None) This also works for tuples of slices >>> fuse_slice((slice(100, 200), slice(100, 200, 10)), ... (slice(10,

(a, b)

def fuse_slice(a, b):
    """Fuse stacked slices together

    Fuse a pair of repeated slices into a single slice:

    >>> fuse_slice(slice(1000, 2000), slice(10, 15))
    slice(1010, 1015, None)

    This also works for tuples of slices

    >>> fuse_slice((slice(100, 200), slice(100, 200, 10)),
    ...            (slice(10, 15), [5, 2]))
    (slice(110, 115, None), [150, 120])

    And a variety of other interesting cases

    >>> fuse_slice(slice(1000, 2000), 10)  # integers
    1010

    >>> fuse_slice(slice(1000, 2000, 5), slice(10, 20, 2))
    slice(1050, 1100, 10)

    >>> fuse_slice(slice(1000, 2000, 5), [1, 2, 3])  # lists
    [1005, 1010, 1015]

    >>> fuse_slice(None, slice(None, None))  # doctest: +SKIP
    None
    """
    # None only works if the second side is a full slice
    if a is None and isinstance(b, slice) and b == slice(None, None):
        return None

    # Replace None with 0 and one in start and step
    if isinstance(a, slice):
        a = normalize_slice(a)
    if isinstance(b, slice):
        b = normalize_slice(b)

    if isinstance(a, slice) and isinstance(b, Integral):
        if b < 0:
            raise NotImplementedError()
        return a.start + b * a.step

    if isinstance(a, slice) and isinstance(b, slice):
        start = a.start + a.step * b.start
        if b.stop is not None:
            stop = a.start + a.step * b.stop
        else:
            stop = None
        if a.stop is not None:
            if stop is not None:
                stop = min(a.stop, stop)
            else:
                stop = a.stop
        step = a.step * b.step
        if step == 1:
            step = None
        return slice(start, stop, step)