max(), min(), arange(), list

[Alt Bayar]

Hello there! 

I am working in Glowscript VPython 2.4. According to help documentations, arange() gives you an ordered sequence (list) of numbers. So I tried this:

#######################################

GlowScript 2.4 VPython

x = arange(-5,5,10/50)

label(text="Max of x: "+max(x))

#######################################

But it doesn't work. What is the problem? Also I tried access the value of x[0] (which I guess is -5) but no success, it returns Undefined.

Thank you.

[Bruce Sherwood]

Interesting. I had not realized that

A = range(3,15,2)

print(A)

gives this result:

{start:3, step:2, stop:15}

Clearly RapydScript-NG in transpiling Python to JavaScript generates a dictionary that is used in for loops but which does not provide list-type access to individual elements. There is no mention of this limitation in the RapydScript-NG documentation, so I'll ask about this.

For the moment the only workaround is to do this:

A = []

for i in range(3,15,2):

    A.append(i)

This will work in both GlowScript VPython and Jupyter VPython.

[Bruce Sherwood]

I reported the issue to the developer of RapydScript-NG, and he has already responded by implementing handling range like a list when appropriate. Kovid Goyal is amazingly responsive. I have some work to do to upgrade to his latest version.

[Sebastian Silva]

El 01/04/17 a las 20:45, Bruce Sherwood escribió:

Hi Bruce et all,

This works for me:

A = list(range(3,15,2))

print(A)

[3, 5, 7, 9, 11, 13]

It works in cpython and rapydscript-ng.

Hope it helps,
Regards,
Sebastian

[Bruce Sherwood]

You're right, that's another possible work-around.

Incidentally, it's interesting in CPython to do this:

a = range(3,15,2)

print(a) # displays "range(3, 15, 2)", not "3, 5, 7, 9, 11, 13"

[Bruce Sherwood]

I upgraded the RapydScript-NG transpiler in GlowScript, and now with r = range(5,7), r[1] is 6.

However, I was surprised that max([5,3,2,13]) gives "undefined" despite the fact that the RS-NG doc says that lists have almost all the functionality of regular Python lists. I've asked about this.

[Bruce Sherwood]

And again Kovid Goyal responded immediately, so min and max methods applied to lists (and to range) are now available.

[Bill Nettles]

x=arange(0.3,pi,0.1)

returns a list of length 5. If one changes the 0.1 step to something else, the length is still 5. x is a list of length 5 no matter what I do with the arange() function in Glowscript VPython

[Bruce Sherwood]

You're right, that's a bug in RapydScript-NG. I've reported it. Thanks.

Bruce

[Bruce Sherwood]

As is so often the case, Kovid Goyal, the lead developer of RapydScript-NG (and of Calibre, a widely used program for converting from one ebook format to another), fixed the range bug just a few hours after I reported it. GlowScript has been updated using his fix.

Bruce

[Bill Nettles]

Beautiful! Thanks for the quick response.