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 = list(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 for the x:y:t type slices, and forcing the user to pass them as strings? Motivation I could just make this example function return something directly sliceable, such as filter(some_condition, some_list), which will be the whole result as a list. In my actual example, however, the internal function is much more complicated, and if I know the slice that the user wants ahead of time, I can greatly simplify the calculation. But I want the user to not have to do much extra to tell me the slice ahead of time. Continue reading...
