Brython - Python in the browser

Pierre Quentel pierre.quentel at
Sat Dec 22 08:57:01 CET 2012

I was over-simplifying - or, to put is less diplomatically, I screwed up - when I answered that the addition returned a string. As Chris pointed out, it made the explanation very confusing. My apologies

The objects handled by + and <= can be :
- strings, integers, floats
- instances of $TagClass instances (more precisely, of classes copied from $TagClass, one for each HTML tag) : they are wrappers around a DOM element. The DOM element itself is the attribute "elt" of the $TagClass instance
- the document, represented by the keyword doc. Its attribute "elt" is the document (top of the DOM tree)
- instances of $AbstractClass, a container with a list of DOM elements. This list is the attribute "children" of the $TagClass instance

Depending of the objects types, a+b returns the following objects :

string + string : string (!)
string + $TagClass : $AbstractTag with children [textNode(a),b.elt]
string + $AbstractTag : $AbstractTag with [textNode(b)]+ b.children

The 2 latter are implemented by the method __radd__ of $TagClass and $AbstractTag, invoqued by the method __add__ of the string class

$TagClass + string : $AbstractTag with [a.elt,textNode(b)]
$TagClass + $TagClass : $AbstractTag with [a.elt,b.elt]
$TagClass + $AbstractTag : $AbstractTag with [a.elt]+b.children
$AbstractTag + string : $AbstractTag with a.children+[textNode(b)]
$AbstractTag + $TagClass : $AbstractTag with a.children + [b.elt]
$AbstractTag + $AbstractTag : $AbstractTag with a.children + b.children

(any type) + doc : unsupported
doc + (any type) : unsupported

The operation x <= y does the following :

string <= (any object) : comparison, if possible

($TagClass | doc) <= string | integer | float : adds textNode(str(y)) to x.elt
($TagClass | doc) <= $TagClass : adds child y.elt to parent x.elt
($TagClass | doc) <= $AbstractTag : adds DOM elements in y.children to x.elt

$AbstractClass <= (any type) : unsupported

- Pierre

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