import urllib2,os
from BeautifulSoup import BeautifulSoup
url = "http://oreilly.com/javascript/excerpts/javascript-good-parts/syntax-diagrams.html"

soup = BeautifulSoup(urllib2.urlopen(url).read())

for _img in soup.findAll('img'):
    if 'excerpts' in _img.get('src'):
        img_url = _img.get('src')
        with open(os.path.basename(img_url), 'wb') as f:
            f.write(urllib2.urlopen(img_url).read())