Question on try/except

[Dan]

While perusing sre.py in the standard library, I came upon this snippet 
of code in the _compile() function definition:

     try:
         p = sre_compile.compile(pattern, flags)
     except error, v:
         raise error, v # invalid expression

Is there some particular use in catching an exception and immediately 
re-raising it?  Why catch it at all?

/Dan

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