Assuming module foo with method bar:
import foo
method_to_call = getattr(foo, 'bar')
result = method_to_call()
You could shorten lines 2 and 3 to:
result = getattr(foo, 'bar')()
if that makes more sense for your use case.
You can use getattr in this fashion on class instance bound methods, module-level methods, class methods... the list goes on.
2015 update: the flexbox approach
There are two other answers briefly mentioning flexbox; however, that was more than two years ago, and they don't provide any examples. The specification for flexbox has definitely settled now.
Note: Though CSS Flexible Boxes Layout specification is at the Candidate Recommendation stage, not all browsers have implemented it. WebKit implementation must be prefixed with -webkit-; Internet Explorer implements an old version of the spec, prefixed with -ms-; Opera 12.10 implements the latest version of the spec, unprefixed. See the compatibility table on each property for an up-to-date compatibility status.
(taken from https://developer.mozilla.org/en-US/docs/Web/Guide/CSS/Flexible_boxes)
All major browsers and IE11+ support Flexbox. For IE 10 or older, you can use the FlexieJS shim.
To check current support you can also see here:
http://caniuse.com/#feat=flexbox
Working example
With flexbox you can easily switch between any of your rows or columns either having fixed dimensions, content-sized dimensions or remaining-space dimensions. In my example I have set the header to snap to its content (as per the OPs question), I've added a footer to show how to add a fixed-height region and then set the content area to fill up the remaining space.
html,
body {
height: 100%;
margin: 0;
}
.box {
display: flex;
flex-flow: column;
height: 100%;
}
.box .row {
border: 1px dotted grey;
}
.box .row.header {
flex: 0 1 auto;
/* The above is shorthand for:
flex-grow: 0,
flex-shrink: 1,
flex-basis: auto
*/
}
.box .row.content {
flex: 1 1 auto;
}
.box .row.footer {
flex: 0 1 40px;
}
<!-- Obviously, you could use HTML5 tags like `header`, `footer` and `section` -->
<div class="box">
<div class="row header">
<p><b>header</b>
<br />
<br />(sized to content)</p>
</div>
<div class="row content">
<p>
<b>content</b>
(fills remaining space)
</p>
</div>
<div class="row footer">
<p><b>footer</b> (fixed height)</p>
</div>
</div>
In the CSS above, the flex property shorthands the flex-grow, flex-shrink, and flex-basis properties to establish the flexibility of the flex items. Mozilla has a good introduction to the flexible boxes model.
Best Solution
The big complication here is emulating the full browser environment outside of a browser. You can use stand alone javascript interpreters like Rhino and SpiderMonkey to run javascript code but they don't provide a complete browser like environment to full render a web page.
If I needed to solve a problem like this I would first look at how the javascript is rendering the page, it's quite possible it's fetching data via AJAX and using that to render the page. I could then use python libraries like simplejson and httplib2 to directly fetch the data and use that, negating the need to access the DOM object. However, that's only one possible situation, I don't know the exact problem you are solving.
Other options include the selenium one mentioned by Łukasz, some kind of webkit embedded craziness, some kind of IE win32 scripting craziness or, finally, a pyxpcom based solution (with added craziness). All these have the drawback of requiring pretty much a fully running web browser for python to play with, which might not be an option depending on your environment.