I fail to see why you can't have both args and kwargs... class BaseException: @classmethod def format(cls, fmt, *args, **kwargs): return cls(fmt.format(*args, **kwargs), *args, **kwargs) And concerning Gerog's actual question, I think this is a not uncommon pattern, but raise Exception.format(...) doesn't sound good. It's not really as readable as raise Exception(fmt.format(ext), ext) ilya suggested an almost ok direction but he doesn't define formats at runtime. So maybe instead we can make a factory for formatted exceptions. def formatted_exception(exception): def format_and_return(fmt, *args, **kwargs): return exception(fmt.format(*args, **kwargs), *args, **kwargs) return format_and_return @formatted_exception class NotRegisteredError(LookupError): pass then the usage becomes: raise NotRegisteredError("Extension {0} not registered.", ext) On Fri, Sep 18, 2009 at 10:54 PM, ilya <ilya.nikokoshev@gmail.com> wrote:
How about simplifying creation of a subclass for this pattern::
class NotRegisteredError(LookupError): template = 'Extension {1} not registered'
... raise NotRegisteredError(ext)
This is instead of::
class NotRegisteredError(LookupError): def __init__(self, *args): super().__init__('Extension {1} not registered'.format(self, *args), *args)
Advantages to having a separate subclass: (1) it can be reused (2) it can be caught separately from LookupError (3) you can list possible exceptions in the beginning of module (4) you can search for functions that raise a specific exception
What do you think?
Ilya.
To make Exceptions where some object(s) are involved more useful, it is often necessary to put the objects on the exception *in addition to* formatting them into a string representation for the message.
This little classmethod would make that easier::
class BaseException: @classmethod def format(cls, fmt, *args): return cls(fmt.format(*args), *args)
Example usage::
ext = 'foo' raise LookupError.format('Extension {0} not registered', ext)
'foo' could then be accessed as ``exc.args[1]``.
A similar, but also very useful implementation would be ::
def format(cls, fmt, **kwds): exc = cls(fmt.format(**kwds)) exc.__dict__.update(kwds) return exc
with example usage being::
raise LookupError.format('Extension {ext} not registered', ext='foo')
and 'foo' being accessible as ``exc.ext``.
I realize this is probably too obscure for Python core, but I wanted to show it to you anyway, maybe it'll be found useful.
Georg
-- Thus spake the Lord: Thou shalt indent with four spaces. No more, no less. Four shall be the number of spaces thou shalt indent, and the number of
indenting shall be four. Eight shalt thou not indent, nor either indent
On Fri, Sep 18, 2009 at 6:07 PM, Georg Brandl <g.brandl@gmx.net> wrote: thy thou
two, excepting that thou then proceed to four. Tabs are right out.
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