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Newsgroups: comp.lang.python
Date: Thu, 20 Dec 2012 01:37:49 -0800 (PST)
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Subject: Re: Brython - Python in the browser
From: Pierre Quentel <pierre.quentel@gmail.com>
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Le jeudi 20 d=E9cembre 2012 01:07:15 UTC+1, Terry Reedy a =E9crit=A0:
> On 12/19/2012 1:19 PM, Pierre Quentel wrote:
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> > The objective of Brython is to replace Javascript by Python as the
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> > scripting language for web browsers, making it usable on all
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> > terminals including smartphones, tablets, connected TVs, etc. Please
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> > forgive the lack of ambition ;-)
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> This sounds similar to pyjs, but the latter has two big problems: a)=20
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> personality conflicts splits among the developers; b) last I knew, it=20
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> was stuck on Python 2.
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It is indeed different from pyjs : both translate Python into Javascript, b=
ut with Brython the translation is done on the fly by the browser, with pyj=
s is is done once by a Python script
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> I think your home page/doc/announcement should specify Python 3 at the=20
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> top, so it is not a mystery until one reads down to
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> "Brython supports most keywords and functions of Python 3 : "
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Done on the home page
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> "lists are created with [] or list(), tuples with () or tuple(),=20
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> dictionaries with {} or dict() and sets with set()"
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> non-empty sets are also created with {} and you should support that.
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Ok, I put this point in the issue tracker
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> > The best introduction is to visit the Brython site
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> > (http://www.brython.info).
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> That says that my browser, Firefox 17, does not support HTML5. Golly=20
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> gee. I don't think any browser support5 all of that moving target, and=20
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> Gecko apparently supports about as large a subset as most.
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> https://en.wikipedia.org/wiki/Comparison_of_layout_engines_%28HTML5%29
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> It is possible the FF still does not support the particular feature=20
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> needed for the clock, but then the page should say just that. Has the=20
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> latest FF (17) actually been tested?
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I changed the error message adding "or Javascript is turned off"
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> > To create an element, for instance an HTML anchor :
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> > doc <=3D A('Python',href=3D"http://www.python.org")
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> To me, that is a awful choice and I urge you to change it.
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> '<=3D' is not just an operator, it is a comparison operator. It normally=
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> return False or True. Numpy array comparison returns arrays of booleans,=
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> so the meaning is extended, not completely changed. People will often be=
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> using it with its normal mean in conditionals elsewhere, so this usage=20
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> creates strong cognitive dissonance. Also, using an expression as a=20
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> statement is allowed, but except in the interactive interpreter, it only=
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> makes sense with an expression that obviously has side-effects or could=
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> have side-effects (like the expression 'mylist.sort()'. It just looks=20
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> wrong to an experienced Python programmer like me.
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> It also is unnecessary. Use '+=3D' or '|=3D'. The former means just what =
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> want the statement to do and the latter is at least somewhat related=20
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> (bit or-addition) and is rarely used and is very unlikely to be used in=
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> code intended for a browser.
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I'm afraid I am going to disagree. The document is a tree structure, and to=
day Python doesn't have a syntax for easily manipulating trees. To add a ch=
ild to a node, using an operator instead of a function call saves a lot of =
typing ; <=3D looks like a left arrow, which is a visual indication of the =
meaning "receive as child". |=3D doesn't have this arrow shape

+=3D is supported by Brython, but it means something different. <=3D means =
"add child" ; the addition operator + means "add brother"

For instance,

d =3D UL(LI('test1'))
d +=3D UL(LI('test2'))
doc <=3D d

will show two unordered lists at the same level, while
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d =3D UL(LI('test1'))
d <=3D UL(LI('test2'))
doc <=3D d

will nest the second list inside the first one

In fact, even in CPython there could be a built-in tree class that could be=
 managed by a syntax such as this one
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> > It still lacks important features of Python, mostly list
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> > comprehensions and classes ;
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> Since Python 3 has 4 types of comprehensions, while Python 2 only has=20
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> list comprehensions, I took this to mean that Brython was Python 2.
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> And yes, I am all in favor of being able to use a subset of Py3 instead=
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> of javascript. A full Python interpreter in a browser is too dangerous.=
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> (Actually, I think javascript is too, but that is a different issue.)=20
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> Python translated to javascript cannot be worse than javascript. I=20
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> presume the same would be true if the javascript step were omitted and=20
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> Python were directly compiled to the virtual machines defined by current=
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> javascript engines.
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> --=20
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> Terry Jan Reedy