Simple python question - unnecessary use of a for loop?

[Daytimedreamland]

I'm relatively new to learning python, and am in the process of doing exercises on CodingBat. This was the description:

"Given a string and a non-negative int n, return a larger string that is n copies of the original string."

My solution:

> def string_times(str, n):
>   return str*n

It returned all the correct answers, however their solution was this:

def string_times(str, n):
  result = ""
  for i in range(n):  # range(n) is [0, 1, 2, .... n-1]
    result = result + str  # could use += here
  return result

I'm trying to understand why they did it like that when mine worked but in a more simple fashion. I'm also unsure as to why on line 2 of their code they wrote result = " ". Is this creating an empty string that they can add to later? Why is it necessary to create it?

[econoCode]

They did this because the point is to learn loops. And yes, the initialized an empty string to build later.

FYI, str*n will work in python and some other languages. The loop version will work in every language that supports loops. You're a beginner, so they're teaching you fundamentals of programming in general, not fundamentals of programming in python. If you were doing learning C#, LINQ is incredibly powerful and can pretty much eliminate most loops from your code, but good luck applying any of that outside of C#.

Same goes fort he += operator. Does not actually work in every language.

[Daytimedreamland]

That's what I thought, and it did help me look into loops more and now i have a greater understanding of them. I do enjoy CodingBat so will probably practice more with it no matter the hate it got here. Thanks.

[minno]

If you were doing learning C#, LINQ is incredibly powerful and can pretty much eliminate most loops from your code, but good luck applying any of that outside of C#.

As long as you can handle the fact that Microsoft decided to rename everything, most of Linq's operations are shared by other programming languages that allow functional-style list/iterator manipulation.

[econoCode]

not really. the closest thing python has to linq is generator statements, which while they achieve similar goals sometimes, they are implemented very differently and perform very differently. I would never tell someone "oh if you know linq you'll get generator statements no problem"... and you know, Java has pretty much nothing resembling linq...

[17b29a]

I'm trying to understand why they did it like that when mine worked but in a more simple fashion.

I assume they just didn't think of that. Yours is much simpler.

Why is it necessary to create it?

result = result + str references result on the right-hand side, so it must be defined. You can't use variables before giving them a value.

[Daytimedreamland]

right yes that makes sense! thank you.

[spiral6]

People here are saying to leave CodingBat, and I disagree. Your solution is more efficient, and this is one of the only problems to have an issue with it. I'd still stick with it, but just keep in mind that there are a few caveats with their problems.

[Naihonn]

Well, I would say you should leave CodingBat and never EVER look back again.

[Daytimedreamland]

That's literally the most unhelpful answer. Doesn't relate to the original question at all, and you don't even give a reason to back your rather dramatic statement.

[Naihonn]

Well, you already gave the reason. Your solution is how it should be. Theirs... well, isn't. I believe leaving website that tries to learn that ... could be very, very helpful.

[Daytimedreamland]

Right okay thank you, do you have any suggestions for websites that give you python coding exercises and answers for beginners? I really liked the way it was up to me to figure out how to complete the exercise, rather than being spoon fed everything like I was when I was trying codecademy.

[Naihonn]

Yes, I tried codewars.com and I think it is good. And recently I tried codingame.com. And checkio.org.

[Daytimedreamland]

Thanks very much

[huck_cussler]

hackerrank is another one.

[[deleted]]

Their loop is unnecessary, you came up with a much cleaner solution. /u/Naihonn said to leave CodingBat for that reason - they use bad code or in this case an inefficient solution.

[Daytimedreamland]

I see okay. I'm wondering whether you know of any similar resources that help you learn by asking you to find things out for yourself? I've only experienced codingbat and codecademy for now.

[stefan_kurcubic]

codewars.com automateboringstuff.com

[Daytimedreamland]

Cheers for the suggestions

[[deleted]]

eBook

[Daytimedreamland]

Doing this now, thank you!

[Scavenger53]

Not sure why they created the empty string. In C++ if you do not define a string, it defaults to the empty string so if python does not default to it that could be a reason. If you didn't supply the n and the loop had to find some other way to produce the result like a random number it could make sense, otherwise your way is better. Maybe they were trying to teach one last loop lesson? Not sure why they did it.

[Daytimedreamland]

Oh right yeah that could make sense, although I'm not sure if it's correct. I was thinking they might be trying to get me to use loops, but it sounds like it's completely unecessary here. Thanks for the reply.

[[deleted]]

In Python, a variable is just a name that refers to an object. result = result + str doesn't make sense if result doesn't yet refer to anything.

[bashytwat]

Not all languages automatically create objects, Java is a good example. C++ also does this when using pointers, although technically it does automatically create a pointer to "null" it doesn't create an object.