Weird exception handling behavior -- late evaluation in except clause

Roy Smith roy at panix.com
Sun Dec 2 18:25:22 CET 2012


This is kind of weird (Python 2.7.3):

try:
    print "hello"
except foo:
    print "foo"

prints "hello".  The problem (IMHO) is that apparently the except clause 
doesn't get evaluated until after some exception is caught.  Which means 
it never notices that foo is not defined until it's too late.

This just came up in some code, where I was trying to catch a very rare 
exception.  When the exception finally happened, I discovered that I had 
a typo in the except clause (I had mis-spelled the name of the 
exception).  So, instead of getting some useful information, I got an 
AttributeError :-(

Is this a bug, or intended behavior?  It seems to me it would be much 
more useful (if slightly more expensive) to evaluate the names of the 
exceptions in the expect clause before running the try block.



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