Why won't .png files download with Python script while it works for other images?
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I am trying to search the source code of a webpage, and download various files from it using Python. This script searches the source code for .jpg files and downloads them all as expected. However, upon modifying the script (changing ".jpg" to ".png", as shown below), I get the error: 

> Traceback (most recent call last):   File "img.py", line 19, in
> <module>
>     urllib.urlretrieve(images[z], "image"+str(z)+".png")   File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/urllib.py",
> line 91, in urlretrieve   File
> "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/urllib.py",
> line 237, in retrieve   File
> "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/urllib.py",
> line 205, in open   File
> "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/urllib.py",
> line 461, in open_file   File
> "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/urllib.py",
> line 475, in open_local_file IOError: [Errno 2] No such file or
> directory: '/images/adapt-icon-search.png?1342791397'


Here is the script I am using:

    import urllib
    import urllib2
    import re
    
    print "enter url of site (such as 'dribbble.com')"
    
    url = raw_input()
    fullurl = "http://"+url
    
    src = urllib2.urlopen(fullurl)
    src = src.read()
    
    images = re.findall('src="(.*\.png[^"]*)', src)
    
    z=0
    while z < len(images):
    	urllib.urlretrieve(images[z], "image"+str(z)+".png")
    	print "done"
    	z+=1
Insight as to why this script doesn't work for .png files would be much appreciated. Many thanks in advance.