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Python Python Collections (Retired) Slices Introduction To Slices

Frances Tang
Frances Tang
24,767 Points
Posted by Frances Tang
Frances Tang
24,767 Points

Slice video 1:49

Hello fellow coders,

I got very confused over the process below:

my_list = list(range(1, 6)) my_list [1, 2, 3, 4, 5] my_list[1: 3]

[2, 3]

So, since the index number is 1 and 3, shouldn't we get [2, 4] instead of [2, 3] from my_list?

And also, why is list(range(1, 6)) is [1, 2, 3, 4, 5], not [1, 2, 3, 4, 5, 6]?

Thank you for your time in advance!

2 Answers

Sam Dale
Sam Dale
6,136 Points
Sam Dale
Sam Dale
6,136 Points

So for list(range(1, 6)) the reason it gives you [1, 2, 3, 4, 5] is because range has the following syntax: range(start, upper_bound). This means that the range will go from the start up until the upper_bound but not including the upper bound. The reason Python does this is that it is very convenient to use len() to write something like:

blah = [1, 2, 3, 4]
for i in range(0, len(blah)):
    print(blah[i])

Now the same principle is at play with the substring. For my_list = [1, 2, 3, 4, 5], and my_list[1:3], goes from the start up until the upper bound, but not including the upper bound. <br>Another way to think about this is if I showed you: 1 <= x < 6. x could be 1, 2, 3, 4, or 5, but x cannot be 6, because it goes up to but doesn't include 6. Hope that helps a little!

Amy-Kate Andrews
Amy-Kate Andrews
26,286 Points
Amy-Kate Andrews
Amy-Kate Andrews
26,286 Points

I agree with Sam Dale (above).

So in the example, list(range(1,6)), when creating a list, 1 is the first number to start the iteration, and 6 is the number that the list will go up to but will not include.

Then when you select from the list, using my_list[1:3], 1 is the starting index (which is zero based), and 3 is the index that the slice will go up to but will not include.