You get the same Exception
as your base problem is "You can't do this" but the details are contained in the exception instance, (or in a string on older pythons), so if you handle the problem as:
try:
outfile = open('somename.txt', 'w')
except IOError, e:
print "Not allowed", e
You will get a lot more information. (N.B. if you are running python 3 you will need to add brackets to the print above).
This is actually incredibly good design - your basic problem is that there is a problem - and you can find out more if you care to - and you can handle a given class of problem in a generalised manner.
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