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How to read a HTML page that takes some time to load? [duplicate]

I am trying to scrape a web site using python and beautiful soup. I encountered that in some sites, the image links although seen on the browser is cannot be seen in the source code. However on using Chrome Inspect or Fiddler, we can see the the corresponding codes.
What I see in the source code is:
<div id="cntnt"></div>
But on Chrome Inspect, I can see a whole bunch of HTML\CSS code generated within this div class. Is there a way to load the generated content also within python? I am using the regular urllib in python and I am able to get the source but without the generated part.
I am not a web developer hence I am not able to express the behaviour in better terms. Please feel free to clarify if my question seems vague !

You need JavaScript Engine to parse and run JavaScript code inside the page.
There are a bunch of headless browsers that can help you
http://code.google.com/p/spynner/
http://phantomjs.org/
http://zombie.labnotes.org/
http://github.com/ryanpetrello/python-zombie
http://jeanphix.me/Ghost.py/
http://webscraping.com/blog/Scraping-JavaScript-webpages-with-webkit/

The Content of the website may be generated after load via javascript, In order to obtain the generated script via python refer to this answer

A regular scraper gets just the HTML document. To get any content generated by JavaScript logic, you rather need a Headless browser that would also generate the DOM, load and run the scripts like a regular browser would. The Wikipedia article and some other pages on the Net have lists of those and their capabilities.
Keep in mind when choosing that some previously major products of those are abandoned now.

TRY THIS FIRST!
Perhaps the data technically could be in the javascript itself and all this javascript engine business is needed. (Some GREAT links here!)
But from experience, my first guess is that the JS is pulling the data in via an ajax request. If you can get your program simulate that, you'll probably get everything you need handed right to you without any tedious parsing/executing/scraping involved!
It will take a little detective work though. I suggest turning on your network traffic logger (such as "Web Developer Toolbar" in Firefox) and then visiting the site. Focus your attention attention on any/all XmlHTTPRequests. The data you need should be found somewhere in one of these responses, probably in the middle of some JSON text.
Now, see if you can re-create that request and get the data directly. (NOTE: You may have to set the User-Agent of your request so the server thinks you're a "real" web browser.)

Webscraping Financial Data from Morningstar

I am trying to scrape data from the morningstar website below:
http://financials.morningstar.com/ratios/r.html?t=IBM&region=USA&culture=en_US
I am currently trying to do just IBM but hope to eventually be able to type in the code of another company and do this same with that one. My code so far is below:
import requests, os, bs4, string
url = 'http://financials.morningstar.com/ratios/r.html?t=IBM&region=USA&culture=en_US';
fin_tbl = ()
page = requests.get(url)
c = page.content
soup = bs4.BeautifulSoup(c, "html.parser")
summary = soup.find("div", {"class":"r_bodywrap"})
tables = summary.find_all('table')
print(tables[0])
The problem I am experiencing at the moment is unlike a simpler webpage I have scraped the program can't seem to locate any tables even though I can see them in the HTML for the page.
In researching this problem the closest stackoverflow question is below:
Python webscraping - NoneObeject Failure - broken HTML?
In that one they explained that Morningstar's tables are dynamically loaded and used some json code I am unfamiliar with and somehow generated a different weblink which managed to scrape the data but I don't understand where it came from?

It's a real problem scraping some modern web pages, particularly on pages generated by single-page applications (where the content is maintained by AJAX calls and DOM modification rather than delivered as ready-to-go HTML in a single server response).
The best way I have found to access such content is to use the Selenium web testing environment to have a browser load the page under the control of my program, then extract the page contents from Selenium for scraping. There are other environments that will execute the scripts and modify the DOM appropriately, but I haven't used any of them.
It's not as difficult as it sounds, but it will take you a little jiggering around to get there.

Web scraping can be greatly simplified when the site offers an API, be it officially supported or just an unofficial hack. Even the hack is better than trying to fiddle with the HTML which can change every day.
So a search for morningstar api might be fruitful. And, in fact, some friendly Gister has already worked this out for you.
Would the search be without result, a usually fruitful approach is to investigate what ajax calls the page is doing to retrieve data and then issue them directly. This can be achieved via the browser debuggers, tab "network" or so where each request can be investigated in detail in a very friendly UI.

I've found scraping dynamic sites to be a lot easier with JavaScript than with Python + Selenium. There is a great module for nodejs/phantomjs: ScraperJS. It is very easy to use: it injects jQuery into the scraped page and you can extract data with jQuery selectors.

Parsing from a website -- source code does not contain the info I need

I'm a little new to web crawlers and such, though I've been programming for a year already. So please bear with me as I try to explain my problem here.
I'm parsing info from Yahoo! News, and I've managed to get most of what I want, but there's a little portion that has stumped me.
For example: http://news.yahoo.com/record-nm-blaze-test-forest-management-225730172.html
I want to get the numbers beside the thumbs up and thumbs down icons in the comments. When I use "Inspect Element" in my Chrome browser, I can clearly see the things that I have to look for - namely, an em tag under the div class 'ugccmt-rate'. However, I'm not able to find this in my python program. In trying to track down the root of the problem, I clicked to view source of the page, and it seems that this tag is not there. Do you guys know how I should approach this problem? Does this have something to do with the javascript on the page that displays the info only after it runs? I'd appreciate some pointers in the right direction.
Thanks.

The page is being generated via JavaScript.
Check if there is a mobile version of the website first. If not, check for any APIs or RSS/Atom feeds. If there's nothing else, you'll either have to manually figure out what the JavaScript is loading and from where, or use Selenium to automate a browser that renders the JavaScript for you for parsing.

Using the Web Console in Firefox you can pretty easily see what requests the page is actually making as it runs its scripts, and figure out what URI returns the data you want. Then you can request that URI directly in your Python script and tease the data out of it. It is probably in a format that Python already has a library to parse, such as JSON.
Yahoo! may have some stuff on their server side to try to prevent you from accessing these data files in a script, such as checking the browser (user-agent header), cookies, or referrer. These can all be faked with enough perseverance, but you should take their existence as a sign that you should tread lightly. (They may also limit the number of requests you can make in a given time period, which is impossible to get around.)

web scraping a problem site

I'm trying to scrape some information from a web site, but am having trouble reading the relevant pages. The pages seem to first send a basic setup, then more detailed info. My download attempts only seem to capture the basic setup. I've tried urllib and mechanize so far.
Firefox and Chrome have no trouble displaying the pages, although I can't see the parts I want when I view page source.
A sample url is https://personal.vanguard.com/us/funds/snapshot?FundId=0542&FundIntExt=INT
I'd like, for example, average maturity and average duration from the lower right of the page. The problem isn't extracting that info from the page, it's downloading the page so that I can extract the info.

The page uses JavaScript to load the data. Firefox and Chrome are only working because you have JavaScript enabled - try disabling it and you'll get a mostly empty page.
Python isn't going to be able to do this by itself - your best compromise would be to control a real browser (Internet Explorer is easiest, if you're on Windows) from Python using something like Pamie.

The website loads the data via ajax. Firebug shows the ajax calls. For the given page, the data is loaded from https://personal.vanguard.com/us/JSP/Funds/VGITab/VGIFundOverviewTabContent.jsf?FundIntExt=INT&FundId=0542
See the corresponding javascript code on the original page:
<script>populator = new Populator({parentId:
"profileForm:vanguardFundTabBox:tab0",execOnLoad:true,
populatorUrl:"/us/JSP/Funds/VGITab/VGIFundOverviewTabContent.jsf?FundIntExt=INT&FundId=0542",
inline:fals e,type:"once"});
</script>

The reason why is because it's performing AJAX calls after it loads. You will need to account for searching out those URLs to scrape it's content as well.

As RichieHindle mentioned, your best bet on Windows is to use the WebBrowser class to create an instance of an IE rendering engine and then use that to browse the site.
The class gives you full access to the DOM tree, so you can do whatever you want with it.
http://msdn.microsoft.com/en-us/library/system.windows.forms.webbrowser(loband).aspx

Scraping Ajax - Using python

I'm trying to scrap a page in youtube with python which has lot of ajax in it
I've to call the java script each time to get the info. But i'm not really sure how to go about it. I'm using the urllib2 module to open URLs. Any help would be appreciated.

Youtube (and everything else Google makes) have EXTENSIVE APIs already in place for giving you access to just about any and all data you could possibly want.
Take a look at The Youtube Data API for more information.
I use urllib to make the API requests and ElementTree to parse the returned XML.

Main problem is, you're violating the TOS (terms of service) for the youtube site. Youtube engineers and lawyers will do their professional best to track you down and make an example of you if you persist. If you're happy with that prospect, then, on you head be it -- technically, your best bet are python-spidermonkey and selenium. I wanted to put the technical hints on record in case anybody in the future has needs like the ones your question's title indicates, without the legal issues you clearly have if you continue in this particular endeavor.

Here is how I would do it: Install Firebug on Firefox, then turn the NET on in firebug and click on the desired link on YouTube. Now see what happens and what pages are requested. Find the one that are responsible for the AJAX part of page. Now you can use urllib or Mechanize to fetch the link. If you CAN pull the same content this way, then you have what you are looking for, then just parse the content. If you CAN'T pull the content this way, then that would suggest that the requested page might be looking at user login credentials, sessions info or other header fields such as HTTP_REFERER ... etc. Then you might want to look at something more extensive like the scrapy ... etc. I would suggest that you always follow the simple path first. Good luck and happy "responsibly" scraping! :)

As suggested, you should use the YouTube API to access the data made available legitimately.
Regarding the general question of scraping AJAX, you might want to consider the scrapy framework. It provides extensive support for crawling and scraping web sites and uses python-spidermonkey under the hood to access javascript links.

You could sniff the network traffic with something like Wireshark then replay the HTTP calls via a scraping framework that is robust enough to deal with AJAX, such as scraPY.