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pythoncustom-exceptions

How to raise my exceptions instead of built-in exceptions?

In some cases, I need to raise my exception because built-in exceptions are not fit to my programs. After I defined my exception, python raises both my exception and built-in exception, how to handle this situation? I want to only print mine?

class MyExceptions(ValueError):
    """Custom exception."""
    pass

try:
    int(age)
except ValueError:
    raise MyExceptions('age should be an integer, not str.')

The output:

Traceback (most recent call last):
  File "new.py", line 10, in <module>
    int(age)
ValueError: invalid literal for int() with base 10: 'merry_christmas'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "new.py", line 12, in <module>
    raise MyExceptions('age should be an integer, not str.')
__main__.MyExceptions: age should be an integer, not str.

I want to print something like this:

Traceback (most recent call last):
  File "new.py", line 10, in <module>
    int(age)
MyException: invalid literal for int() with base 10: 'merry_christmas'
Solution

  • Add from None when raising your custom Exception:

    raise MyExceptions('age should be an integer, not str.') from None

    See PEP 409 -- Suppressing exception context for more information.