Passing Python slice syntax around to functions

Question

In Python, is it possible to encapsulate exactly the common slice syntax and pass it around? I know that I can use `slice` or `__slice__` to emulate slicing. But I want to pass the exact same syntax that I would put in the square brackets that would get used with `__getitem__`. For example, suppose I wrote a function to return some slice of a list. ``` def get_important_values(some_list, some_condition, slice): elems = filter(some_condition, some_list) return elems[slice] ``` This works fine if I manually pass in a slice object: ``` In [233]: get_important_values([1,2,3,4], lambda x: (x%2) == 0, slice(0, None)) Out[233]: [2, 4] ``` But what I want to let the user pass is exactly the same slicing they would have used with `__getitem__`: ``` get_important_values([1,2,3,4], lambda x: (x%2) == 0, (0:-1) ) # or get_important_values([1,2,3,4], lambda x: (x%2) == 0, (0:) ) ``` Obviously this generates a syntax error. But is there any way to make this work, without writing my own mini parser…

Accepted Answer

Perhaps something along the following lines would work for you:

```
class SliceMaker(object):
  def __getitem__(self, item):
    return item

make_slice = SliceMaker()

print make_slice[3]
print make_slice[0:]
print make_slice[:-1]
print make_slice[1:10:2,...]
```

The idea is that you use `make_slice[]` instead of manually creating instances of `slice`. By doing this you'll be able to use the familiar square brackets syntax in all its glory.

Passing Python slice syntax around to functions

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