Question

I need to set a subset of a list to a specific value based on a tuple with bounds (start,end).

Currently I’m doing this:

indexes = range(bounds[0], bounds[1] + 1)
for i in indexes:
   my_list[i] = 'foo'

This doesn’t seem good to me. Is there a more pythonic approach?

Answer 1

Use slice assignment:

my_list[bounds[0]:bounds[1] + 1] = ['foo'] * ((bounds[1] + 1) - bounds[0])

or using local variables to add your + 1 only once:

lower, upper = bounds
upper += 1
my_list[lower:upper] = ['foo'] * (upper - lower)

You may want to store the upper bound as non-inclusive, to play better with python and avoid all the + 1 counts.

Demo:

>>> my_list = range(10)
>>> bounds = (2, 5)
>>> my_list[bounds[0]:bounds[1] + 1] = ['foo'] * ((bounds[1] + 1) - bounds[0])
>>> my_list
[0, 1, 'foo', 'foo', 'foo', 'foo', 6, 7, 8, 9]