Python try...except comma vs 'as' in except

python python-2.6
Peter Graham picture Peter Graham · Mar 29, 2010 · Viewed 90.6k times · Source

What is the difference between ',' and 'as' in except statements, eg:

try:
    pass
except Exception, exception:
    pass

and:

try:
    pass
except Exception as exception:
    pass

Is the second syntax legal in 2.6? It works in CPython 2.6 on Windows but the 2.5 interpreter in cygwin complains that it is invalid.

If they are both valid in 2.6 which should I use?

Answer

Amber picture Amber · Mar 29, 2010

The definitive document is PEP-3110: Catching Exceptions

Summary:

  • In Python 3.x, using as is required to assign an exception to a variable.
  • In Python 2.6+, use the as syntax, since it is far less ambiguous and forward compatible with Python 3.x.
  • In Python 2.5 and earlier, use the comma version, since as isn't supported.

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