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lf in reply to @wence
were you saying my function was very C-like?

i've actually just re-written it and it's almost bang on the same as yours with enumerate - had seen a few people talking about that so tried to get that working. still not entirely sure what the :: does in grid[::d], apart from take every d'th y.

my function:
```
def findTrees2(funcdata, dx, dy):
    numTrees = 0
    for i, line in enumerate(funcdata[::dy]):
        if line[(i*dx) % len(line)] == '#': numTrees += 1
    return numTrees
```
edit: was also confused as to why you can't print an enumerate object until you put it into a list. but guess that's a conversation for data structures... i should really do a bit more formal learning

•

wence in reply to @lf
were you saying my function was very C-like?

Yeah, in the sense of explicit iteration variables for i in range(...).

foo[::d] is shorthand for foo[slice(None, None, d)] so it's indexing with a slice object with a stride of d.

was also confused as to why you can't print an enumerate object until you put it into a list

Iterations over objects in python3 almost always produce generators, which are objects that you can iterate over but produce their results lazily.

Imagine that the code you had written did something like:
```
for i, line in enumerate(funcdata[::dy]):
   if line == "something":
      break # exit early
```
With an eager generator, you have to make all the pairs to iterate over only to discard most of them when you exit early. With a lazy generator, you can avoid that (and can even deal with an infinite stream of data as long as you terminate at some point).

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lf in reply to @wence

Interesting - that probably stems somewhat from 'learning' to code with Java, VBA and then R at university (maths/stats), then trying to pick up Python in recent years. Most of my stuff i've done at work has been VBA in spreadsheets with financial data. I've never really learned properly how to write more advanced programs, all of the main stuff etc just confuses me.

Explanation on enumerate makes sense and thanks for that, very helpful!

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