slice iterator

islice.py

#!/usr/bin/env python3

"""
islice mixin -- makes an easy to access slice-style iterator

"""


class slice_list(list):

    @property
    def islice(self):
        return ISlice(self)


class islice_mixin:
    @property
    def islice(self):
        return ISlice(self)


class ISlice:
    """
    mixin that adds an iterable acces with slice semantics
    """

    def __init__(self, seq):
        self.seq = seq

    def __iter__(self):
        self.current = self.start - self.stride
        return self

    def __next__(self):
        print("in next")
        self.current += self.stride
        if ((self.stride > 0 and self.current >= self.stop) or
            (self.stride < 0 and self.current <= self.stop)):
            raise StopIteration
        return self.seq[self.current]

    def __getitem__(self, slc):
        print("in index")
        print(slc)
        if not isinstance(slc, slice):
            raise TypeError(".islice only works with single slices")
        self.start, self.stop, self.stride = slc.indices(len(self.seq))
        print(self.start, self.stop, self.stride)
        return self

test_islice.py

"""
test code for islice
"""

import pytest

from islice import ISlice, slice_list, islice_mixin


@pytest.fixture
def simple_list():
    return slice_list([2, 4, 3, 5, 6, 7, 3, 8, 2])


@pytest.fixture
def tuple_mixedin():
    class slice_tuple(tuple, islice_mixin):
        pass
    return slice_tuple((4, 6, 2, 8, 3, 5, 6))


def test_islice():
    isl = ISlice([1, 2, 3])
    slicer = isl[:]
    print(slicer)


def test_slice_list1(simple_list):
    l2 = []
    for i in simple_list.islice[:]:
        print(i)
        l2.append(i)
    assert l2 == simple_list


def test_slice_simple_index(simple_list):
    with pytest.raises(TypeError):
        simple_list.islice[4]


def test_slice_stride(simple_list):
    result = list(simple_list.islice[::2])
    assert result == simple_list[::2]


def test_slice_negative(simple_list):
    result = list(simple_list.islice[::2])
    assert result == simple_list[::2]


def test_slice_reverse(simple_list):
    result = list(simple_list.islice[::-1])
    assert result == simple_list[::-1]


def test_mixedin(tuple_mixedin):
    result = tuple(tuple_mixedin[:2:-1])
    assert result == tuple_mixedin[:2:-1]