I'm using scipy.ndimage.label and scipy.ndimage.find_objects to find things in an image. It returns an array of slices. I am trying to get the coordinates of the object out of the slice but can't seem to find a way to get inside the slice object. Here is a simple example:
a = 1
b = 2
c = 13
d = 47
j = slice(a,b,None)
k = slice(c,d,None)
x = (j, k)
print(x)
print(x[0])
print(x[0].indices(2))
print(x[1].indices(2))
Output is:
(slice(1, 2, None), slice(13, 47, None))
slice(1, 2, None)
(1, 2, 1)
(2, 2, 1)
Basically I am looking for the ability to get the values for a, b, c, and d if I'm only given the slice tuple x. I thought indices would get me on the way but I'm not understanding it's behavior.
Are you looking for the start
, stop
and step
properties?
>>> s = slice(1, 2, 3)
>>> s.start
1
>>> s.stop
2
>>> s.step
3
slice.indices
computes the start/stop/step for the indices that would be accessed for an iterable with the input length. So,
>>> s = slice(-1, None, None)
>>> s.indices(30)
(29, 30, 1)
Which means that you would take item 29 from the iterable. It is able to be conveniently combined with xrange
(or range
):
for item in range(*some_slice.indices(len(sequence))):
print(sequence[item])
As a concrete example:
>>> a = range(30)
>>> for i in a[-2:]:
... print(i)
...
28
29
>>> s = slice(-2, None, None)
>>> for ix in range(*s.indices(len(a))):
... print(a[ix])
...
28
29
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