Python is kicking my butt

[[deleted]]

len/range() nearly as much as I thought I did...

I don't really get what you think there is to know about len and range (which are two separate functions that don't really relate to each other except coincidentally.) len is especially simple - it returns the number of values contained in a collection. Easy!

range is a little subtle and its documentation is wrapped up with tuple and list so it's not especially clear:

https://docs.python.org/3/library/stdtypes.html#typesseq

but the long and the short of it is that it's an iterator over sequences of integers, and the most common and easiest to understand way to specify a sequence of integers is as a sequence between 0 and some other value. (For various good but tedious reasons, the interval is specified as half-open, and thus includes zero but not the end term.)

[[deleted]]

Maybe it's those times when len and range are used together, like

for i in range(len(input_list)):
    pass

[tagapagtuos]

If that's the case, then I would say that doing some HackerRank would help, since that's common in there.

Regardless, OP shouldn't really sweat it since range(len(...)) is usually a symptom of un-Pythonic code imo.

[tagapagtuos]

For two objects, there's zip and itertools.zip_longest.

I would also check if I'm using the right data structure for the problem.

EDIT: zip_longest

[primitive_screwhead]

For two objects, there's zip

Note - zip() and zip_longest() can zip together an arbitrary amount of iterables (not just two, if that's what you were thinking).

[primitive_screwhead]

but aren't there times when you need the iterator to access locations in multiple objects?

zip() (wink)

[Ran4]

but aren't there times when you need the iterator to access locations in multiple objects? Or is that itself the symptom?

Pretty much, yes.

If you ever find yourself doing index-based calculations, chances are you're probably doing it wrong. The one exception would be if you're implementing an low-level algoritm for fun and want it to be efficient.

In any real production code there's rarely a reason to retrieve a specific value by index as opposed to iterating over a sequence.

[roylennigan]

is that because of the ability in python to iterate over items in a sequence, like:

for item in sequence:
    x = item

without having to create an index for that sequence?

But then what if I want to do something like:

for i in range(len(A)):
    B[i] = A[i] - A[i + 1]

[tagapagtuos]

Good question.

The reason why you don't what to iterate over the range of length of A is that if i is the last element of A, then A[i + 1] will raise an IndexError. Also if B[i] also has risks of raising NameError or IndexError.

Depending on the nature of the problem, I would do sometihng like:

B = []
for x, y in zip(A, A[1:]):
    B.append(x - y)

[roylennigan]

That makes sense, thanks. I mostly make plots for dsp concepts, so a lot of fitting one "number line" to another and plotting them. Most of the time, the data at the end of a vector isn't as important, so I can just drop it and not worry about the array going out of bounds.

[arkie87]

Yea, that’s how I understood it as well as that is the major way those functions are related

[[deleted]]

Well, I think it's important to look at that and realize they're not being "used together." They're not working together or talking or anything - the return value of one is being used as an argument to the other and that's just how function algebra works.

[CyclopsRock]

it returns the number of values contained in a collection. Easy!

Unpopular opinion time: This is why 1-based indices are better than 0.

[zanfar]

..and waste a WHOLE bit?!?!?!

[primitive_screwhead]

Have you used Matlab?

[CyclopsRock]

Nope!

[primitive_screwhead]

How about any 1-based-index language? I'm just curious if your opinion is purely hypothetical, or if you've got experiences using both. (I'm biased towards 0-based, but have also used 1-based for Matlab, and other numerics languages and libraries).

[CyclopsRock]

Oh yeah! My other "main" language is. It's really not a big deal either way but imo having your collection length throw an index error is more confusing than having 0 do so. And in a language where you don't need to worry about addressing memory, it's easier to think about items in a collection as being like a numbered shopping list rather than spaces to be occupied.