The slice syntax is a handy way to refer to sub-parts of sequences – typically strings and lists. The slice s[start:end] is the elements beginning at start and extending up to but not including end.
E.g
letters = ['a', 'b', 'c', 'd', 'e', 'f', 'g']
print(letters[2:5])
This will give Output : ['c', 'd', 'e']
But how does extended slicing work.
print(letters[2:4:5])
The above print statement will give ['c'] as output. I can't understand how?
That is because the 3rd parameter is called "step"
(start:end:step)
When you say:
print(letters[2:4:5])
Basically you are saying, start at index 2, end at 4 and step 5 times.
For example:
print(letters[::2])
Returns ['a', 'c', 'e', 'g']
Two things to note:
1) In your case, even if you said print(letters[2:4:1000]) the output would still be 'c'
2) Default "step" value is 1.
The slice will essentially work as a step value. Let us assume we have a list of numbers from 1-10. The additional slice will simply work like a "step" value. Here's an example:
nums = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
print(nums[0:10:2])
We step by 2 each time. Here is our output:
[1, 3, 5, 7, 9]
You get C as your output because You are calling the third index, and then slicing up to the 5th index (index 4 since indexes in Python are zero-based), but you are stepping by a value of 5. So you can't step by 5, because that goes past the index that your slice stops at (index 5, or index 4 in zero-based Python syntax). That is why your code only returns 'c'.
