"Up to but not including" (My personal guide on slicing & indexing)

[micseydel]

Therefore, the len() method is inclusive.

I wouldn't say it this way. What would it mean for len to be exclusive, rather than inclusive? That it would actually be the length - 1? Why would you ever have a function for getting the length of something that returns that number minus 1? Don't think of len as inclusive - it doesn't do what the range or randint do, and we shouldn't try to reuse terminology that doesn't fit.

For string and list slicing it begins at the index position specified (including 0) yet is always exclusive.

The way I tend to remember this is that the following function always returns true:

def f(n):
    return len(list(range(n))) == n

When Python was designed, this was intentional - range(n) generates n elements. I believe the rationale was that this would be the most common use case, and so should be the easiest to learn.

For randint() parameters, it is similar to len() with counting begining where specified, inclusive of 0 (if there is a 0).

Just to repeat: I wouldn't think of it as "similar to len" (as what they do is very different). While there's an argument that range() would be inclusive, I don't believe that a similar argument exists for randint. Why would you tell randint a number bigger than what you actually want, just for it to subtract from that? There's no reason for such a thing.

For range() parameters it is like slicing.

This is a fair comparison. I believe the rationale for slicing was similar, in that [icopde]slicable[:n][/icode] is going to be length n. Just as with range, I believe there's a reasonable argument why it could be inclusive, but it's probably good that the two are consistent with each other. (As a side note: try evaluating [icode]list(range(10))[:20][icode] if you're not sure of what the result will be; I don't have any additional commentary on this other than finding it interesting.)

I think I've communicated my intuitions here, which are based on ~14 years of Python. Hopefully they're of use, and if they're not, hopefully someone has a correction for me :)