square brackets after a function call

Question

I am a total novice at Python, and have come across a piece of code that confuses me.

ts, pkt2 = capPort2.wait(1, 45)[0]

The previous line

Answer 1

This means that return value of the wait function is either list or tuple and 0 it is an index of the element from this output. For example:

def func(numericValue):
    return list(str(numericValue))

res = func(1000)
res[0] - > 1

Or:

def convert(value, to_type):
    #do something
    return resuls, convertedValue

res = convert(1100, str)
res[0] - > True

Answer 2

Ah, I think this question answered my own recently, but I would like to extend the answer some:

This call:

var value = getUrlVars()["logout_url"];

would end up setting the variable to the value of the 'logout_url' name-value pair that is returned from the function call to 'getUrlVars()', right? So you don't have to use just a numeric index, it can be used on hash/associative arrays/dictionary/etc results from the function.

So if this is the function 'getUrlVars':

function getUrlVars() {
    var vars = {};
    var parts = window.location.href.replace (/[?&]+([^=&]+)=([^&]*)/gi, function(m,key,value) {
            vars[key] = value;
        }
    );
    return vars;
}

Which is returning key value pairs (from an input URL of ""http://a.place.com/page.html?name=fred&place=b3&logout_url=some.thing.net/go/here/file.html"), e.g.:

'name'='fred',
'place'='b3',
'logout_url'='some.thing.net/go/here/file.html'         <-- URL encoded, most likely

So my function call above would return "some.thing.net/go/here/file.html", while one that looks like this:

getUrlVars()["name"]

would return:

"fred"

I think. :)

-- C

Answer 3

It means to extract the first item in the list/tuple return by the function.

In [1]: "this is a long sentence".split()
Out[1]: ['this', 'is', 'a', 'long', 'sentence']

In [2]: "this is a long sentence".split()[0]
Out[2]: 'this'