How to create a custom Exception with error message and status code in python3

Question

I am trying to create the following exception and call it in another function:

### The exception
class GoogleAuthError(Exception):
    def __init__(self, message, code=403):
        self.code = code
        self.message = message

### Generating the exception
raise GoogleAuthError(message="There was an error authenticating")

### printing the exception
try:
    do_something()
except GoogleAuthError as e:
    print(e.message)

Basically, I want it to print "There was an error authenticating". How would I do this properly, or is the above the correct way to do it?

Patrick Haugh · Accepted Answer · 2018-10-05 17:25:12Z

3

Remove the code argument from your __init__. You aren't using it.

You can also delegate the handling of the error message to the parent Exception class, which already knows about messages

class GoogleAuthError(Exception):
    def __init__(self, message):
        super().__init__(message)
        self.code = 403

try:
    raise GoogleAuthError('There was an error authenticating')
except GoogleAuthError as e:
    print(e)

# There was an error authenticating

answered Oct 5, 2018 at 17:25

Patrick Haugh

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5 Comments

wim Over a year ago

Also worth mentioning: exception message attribute has been deprecated since the dinosaurs roamed the earth. Only *args are considered.

Aran-Fey Over a year ago

@wim Not sure how that is relevant, since the OP defined their own message attribute. That one certainly isn't deprecated.

wim Over a year ago

@Aran-Fey It's relevant because this code doesn't (and shouldn't) assign a message attribute on the exception instance, which is something that deviates from the OP's original API ... I think that's worth mentioning, don't you?

Aran-Fey Over a year ago

@wim Not sure. How could assigning something to message cause a problem? Unless it used to be a read-only attribute, I don't see what could go wrong.

wim Over a year ago

If the OP has a bunch of code which is printing or logging an err.message (similar as shown in the question), they will need to modify that code because there is no longer a message attribute.

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