Python exception syntax difference?

Question

I am just being curious about the syntax of python exceptions as I can't seem to understand when you are suppossed to use the syntax below to catch an exception.

try:
    """
      Code that can raise an exception...
    """
 except Exception as e:
     pass

and

try:
    """
      Code that can raise an exception...
    """
 except Exception, e:
     pass

What is the difference?

I guess I wasn’t keen thanks @MartijnPieters – Bwire Dec 14 '13 at 11:38 — Bwire, Dec 14 '13 at 11:38

score 4 · Accepted Answer · edited Oct 31 '16 at 20:04

4

Note: As Martijn points out, comma variable form is deprecated in Python 3.x. So, its always better to use as form.

As per http://docs.python.org/2/tutorial/errors.html#handling-exceptions

except Exception, e:

is equivalent to

except Exception as e:

Commas are still used when you are catching multiple exceptions at once, like this

except (NameError, ValueError) as e:

Remember, the parentheses around the exceptions are mandatory when catching multiple exceptions.

edited Oct 31 '16 at 20:04

quornian

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answered Dec 14 '13 at 11:34

thefourtheye

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Except that the latter is preferred, the former deprecated and completely removed in Python 3. – Martijn Pieters Dec 14 '13 at 11:34
1

Your last line shows **why** `as` was introduced to replace the comma. It was confusing as hell when multiple exceptions were being caught. Use `except (NameError, ValueError) as e:` there. – Martijn Pieters Dec 14 '13 at 11:35
@MartijnPieters Got you :) Updated it – thefourtheye Dec 14 '13 at 11:36
1

It was common to write the latter as `except NameError, ValueError:` and wonder why it didn't work, or use `except (NameError, e):` and wonder why you still got a `NameError` on `e`. – Martijn Pieters Dec 14 '13 at 11:37
1

You are still implying that you can only catch multiple exceptions with the now-deprecated syntax. – Martijn Pieters Dec 14 '13 at 11:37

score 1 · Answer 2 · answered Dec 14 '13 at 11:33

1

except Exception, e is deprecated in Python 3.

The proper form is:

try:
    ...
except Exception as e:
    ...

See: http://docs.python.org/3.0/whatsnew/2.6.html#pep-3110

answered Dec 14 '13 at 11:33

James Mills

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The comma form is not just deprecated in Python 3; it is **removed** altogether. – Nayuki Nov 16 '21 at 05:29

Python exception syntax difference?

2 Answers2