Understanding the Difference Between ',' and 'as' in Python Exception Handling

When working with Python's error handling, you may encounter two syntaxes in except statements: ',' and 'as'. This article aims to clarify the difference between these two syntaxes and guide their appropriate use.

Syntax with a Comma

try:
    pass
except Exception, exception:
    pass

In Python versions prior to 2.6, this syntax was the only way to assign an exception to a variable. The comma separates the exception class from the variable name. For example, the above code would assign the exception to the variable exception.

Syntax with 'as'

try:
    pass
except Exception as exception:
    pass

Introduced in Python 2.6, the as syntax allows for clearer and more explicit assignment of an exception to a variable. This syntax assigns the exception to the variable specified after the keyword as. Continuing the example above, this code assigns the exception to the variable exception.

Legal Syntax for Different Python Versions

The legality of the as syntax depends on the Python version:

• Python 2.5 and earlier: Only the comma syntax is valid.
• Python 2.6 and later: Both the comma and as syntaxes are valid.
• Python 3.x: The as syntax is required.

Recommendation for Use

While both syntaxes are valid in Python 2.6 , it is recommended to use the as syntax. It is less ambiguous and forward compatible with Python 3.x, where it becomes the required syntax.