Re: How to get outer class name from an inner class?
On May 9, 6:05 am, John Gordon gor...@panix.com wrote: I'd like to group the classes underneath a parent class, like so: class Question(ApplicationException): class TooShort(ApplicationException): pass class TooLong(ApplicationException): pass This will make it easier in the future for organizing lots of sub-errors. My problem is this: the get_message() method in the base class only knows the current class name, i.e. TooShort or TooLong. But that's not enough; I also need to know the outer class name, i.e. Question.TooShort or Question.TooLong. How do I get the outer class name? This might do the trick: import inspect def exception_members(scope): classes = (m[1] for m in inspect.getmembers(scope, inspect.isclass)) return set( c for c in classes if Exception in c.__mro__ ) class ApplicationException(Exception): @property def outer_scope(self): for _class in exception_members(inspect.getmodule(self.__class__)): if self.__class__ in exception_members(_class): return _class def get_message(self): scope = self.outer_scope class_name = scope.__name__ + '.' if scope else '' class_name += self.__class__.__name__ return class_name When get_message is run, it looks in the module where the exception was defined for any new classes derived from Exception, then looks at the members of each of those to see if it matches the current object's class. Not really well tested, so beware :) -- http://mail.python.org/mailman/listinfo/python-list
Re: How to get outer class name from an inner class?
Am 08.05.2012 22:05, schrieb John Gordon: [...] class QuestionTooShortError(ApplicationException): User entered a security question which is too short. pass class QuestionTooLongError(ApplicationException): User entered a security question which is too long. pass This scheme works, but I'd like to make it more streamlined. Specifically, I'd like to group the classes underneath a parent class, like so: class Question(ApplicationException): class TooShort(ApplicationException): pass class TooLong(ApplicationException): pass This will make it easier in the future for organizing lots of sub-errors. What is it that this parent class represents? What is the relation between class Question and class TooShort? In general terms, it isn't even a parent class but just an outer class, a parent class implies that child classes inherit from it. I think that you're going about this the wrong way, and that a module represents much better what you are trying to express here. Your code actually looks a bit like it was written with a strong Java or C++ background, could that be the case? My problem is this: the get_message() method in the base class only knows the current class name, i.e. TooShort or TooLong. But that's not enough; I also need to know the outer class name, i.e. Question.TooShort or Question.TooLong. How do I get the outer class name? # in module Question class _Exception(ApplicationException): def get_message(self): return self._lookup_message(Question. + self.__class__.__name__) class TooLong(_Exception): pass You might even be able to look up the module name instead of hard-coding it in one place. Uli -- http://mail.python.org/mailman/listinfo/python-list
Re: How to get outer class name from an inner class?
On May 8, 4:05 pm, John Gordon gor...@panix.com wrote: I'm trying to come up with a scheme for organizing exceptions in my application. Currently, I'm using a base class which knows how to look up the text of a specific error in a database table, keyed on the error class name. The base class looks like this: class ApplicationException(Exception): Base class for application-specific errors. def get_message(self): Return the error message associated with this class name. class_name = self.__class__.__name__ return UserMessage.objects.get(key=class_name).text And then I define a bunch of subclasses which all have different names: class QuestionTooShortError(NetIDAppsError): User entered a security question which is too short. pass class QuestionTooLongError(NetIDAppsError): User entered a security question which is too long. pass This scheme works, but I'd like to make it more streamlined. Specifically, I'd like to group the classes underneath a parent class, like so: class Question(ApplicationException): class TooShort(ApplicationException): pass class TooLong(ApplicationException): pass This will make it easier in the future for organizing lots of sub-errors. It's no more or less organized than using a module, so use a module. This is why they exist, after all. That being said, this seems like a bad idea to me: this is a lot of code and types just for a message lookup! Exception types should usually be created based on what you expect users to catch, not based on what you could throw. If all of these exceptions will be handled in the same way, then they shouldn't be distinct types. Adam -- http://mail.python.org/mailman/listinfo/python-list
Re: How to get outer class name from an inner class?
John Gordon wrote:
I'm trying to come up with a scheme for organizing exceptions in
my application.
Currently, I'm using a base class which knows how to look up the text
of a specific error in a database table, keyed on the error class name.
The base class looks like this:
class ApplicationException(Exception):
Base class for application-specific errors.
def get_message(self):
Return the error message associated with this class name.
class_name = self.__class__.__name__
return UserMessage.objects.get(key=class_name).text
And then I define a bunch of subclasses which all have different names:
class QuestionTooShortError(NetIDAppsError):
User entered a security question which is too short.
pass
class QuestionTooLongError(NetIDAppsError):
User entered a security question which is too long.
pass
This scheme works, but I'd like to make it more streamlined. Specifically,
I'd like to group the classes underneath a parent class, like so:
class Question(ApplicationException):
class TooShort(ApplicationException):
pass
class TooLong(ApplicationException):
pass
This will make it easier in the future for organizing lots of sub-errors.
My problem is this: the get_message() method in the base class only knows
the current class name, i.e. TooShort or TooLong. But that's not
enough; I also need to know the outer class name, i.e. Question.TooShort
or Question.TooLong. How do I get the outer class name?
Thanks,
You're going way too much into details regarding your exceptions.
Basically, you need to create an exception class is at some point you
need different handlers.
For instance,
try:
whatever()
except Question.TooShort:
dosomething()
except Question.TooLong:
dosomethingelse()
But I'm not sure you really need this.
Try to keep it simple.
You fetch you exception message from a database, is that really required
? Why can't you just write it in your code ?
Another problem is getting the database key from the class name, this
makes difficult changing any class name, I'm not sure this is a good idea.
Anyway I'm not sure I'm helping here, providing more questions than answer.
What you could do :
class AppException(Exception): pass
class Question(AppException): pass
class TooShort(Question): pass
class TooLong(Question): pass
def getName(cls):
if not hasattr(cls, '__base__'):
raise ValueError('Not a new class style')
if cls is AppException:
return cls.__name__
return getName(cls.__base__)+'.' + cls.__name__
getName(TooShort)
'AppException.Question.TooShort'
This implies you're using only inheritance, not using class as
ccontainer/namespace.
JM
--
http://mail.python.org/mailman/listinfo/python-list
How to get outer class name from an inner class?
I'm trying to come up with a scheme for organizing exceptions in my application. Currently, I'm using a base class which knows how to look up the text of a specific error in a database table, keyed on the error class name. The base class looks like this: class ApplicationException(Exception): Base class for application-specific errors. def get_message(self): Return the error message associated with this class name. class_name = self.__class__.__name__ return UserMessage.objects.get(key=class_name).text And then I define a bunch of subclasses which all have different names: class QuestionTooShortError(NetIDAppsError): User entered a security question which is too short. pass class QuestionTooLongError(NetIDAppsError): User entered a security question which is too long. pass This scheme works, but I'd like to make it more streamlined. Specifically, I'd like to group the classes underneath a parent class, like so: class Question(ApplicationException): class TooShort(ApplicationException): pass class TooLong(ApplicationException): pass This will make it easier in the future for organizing lots of sub-errors. My problem is this: the get_message() method in the base class only knows the current class name, i.e. TooShort or TooLong. But that's not enough; I also need to know the outer class name, i.e. Question.TooShort or Question.TooLong. How do I get the outer class name? Thanks, -- John Gordon A is for Amy, who fell down the stairs gor...@panix.com B is for Basil, assaulted by bears -- Edward Gorey, The Gashlycrumb Tinies -- http://mail.python.org/mailman/listinfo/python-list
Re: How to get outer class name from an inner class?
In jobua0$m3f$1...@reader1.panix.com John Gordon gor...@panix.com writes: class QuestionTooShortError(NetIDAppsError): User entered a security question which is too short. pass class QuestionTooLongError(NetIDAppsError): User entered a security question which is too long. pass Oops! These classes inherit from ApplicationException, not NetIDAppsError. -- John Gordon A is for Amy, who fell down the stairs gor...@panix.com B is for Basil, assaulted by bears -- Edward Gorey, The Gashlycrumb Tinies -- http://mail.python.org/mailman/listinfo/python-list
Re: How to get outer class name from an inner class?
On Tue, May 8, 2012 at 1:05 PM, John Gordon gor...@panix.com wrote: I'm trying to come up with a scheme for organizing exceptions in my application. Currently, I'm using a base class which knows how to look up the text of a specific error in a database table, keyed on the error class name. The base class looks like this: class ApplicationException(Exception): Base class for application-specific errors. def get_message(self): Return the error message associated with this class name. class_name = self.__class__.__name__ return UserMessage.objects.get(key=class_name).text And then I define a bunch of subclasses which all have different names: class QuestionTooShortError(NetIDAppsError): User entered a security question which is too short. pass class QuestionTooLongError(NetIDAppsError): User entered a security question which is too long. pass This scheme works, but I'd like to make it more streamlined. Specifically, I'd like to group the classes underneath a parent class, like so: class Question(ApplicationException): class TooShort(ApplicationException): pass class TooLong(ApplicationException): pass This will make it easier in the future for organizing lots of sub-errors. You could use modules instead… Nested classes are stylistically questionable. My problem is this: the get_message() method in the base class only knows the current class name, i.e. TooShort or TooLong. But that's not enough; I also need to know the outer class name, i.e. Question.TooShort or Question.TooLong. How do I get the outer class name? Use __qualname__ and chop off the last dotted part (i.e. the innermost class' name, thus yielding its parent's name). PEP 3155 -- Qualified name for classes and functions: http://www.python.org/dev/peps/pep-3155/ Cheers, Chris -- http://mail.python.org/mailman/listinfo/python-list
Re: How to get outer class name from an inner class?
On 5/8/2012 4:05 PM, John Gordon wrote:
I'm trying to come up with a scheme for organizing exceptions in
my application.
Currently, I'm using a base class which knows how to look up the text
of a specific error in a database table, keyed on the error class name.
The base class looks like this:
class ApplicationException(Exception):
Base class for application-specific errors.
def get_message(self):
Return the error message associated with this class name.
class_name = self.__class__.__name__
return UserMessage.objects.get(key=class_name).text
And then I define a bunch of subclasses which all have different names:
class QuestionTooShortError(NetIDAppsError):
User entered a security question which is too short.
pass
class QuestionTooLongError(NetIDAppsError):
User entered a security question which is too long.
pass
This scheme works, but I'd like to make it more streamlined. Specifically,
I'd like to group the classes underneath a parent class, like so:
class Question(ApplicationException):
class TooShort(ApplicationException):
pass
class TooLong(ApplicationException):
pass
This will make it easier in the future for organizing lots of sub-errors.
I think maybe you are being much too fine-grained in your exception
hierarchy. Python has, for instance, just one ValueError, with details
in the error. The details can include specific values only known at the
point of the error. You are putting some specifics in the exception name
and then (apparently) given them somewhat redundant canned messages
lacking situation-specific details.
For instance
errfmt = Security question length {:d} not in legal range {:d} - {:d}
if not (secquemin = len(secque) = secquemax):
raise ValueError(errfmt.format(len(secque), secquemin, secquemax))
# or ApplicationError or AppValueError if you want.
The messages in Python are not this good, but they slowly improve as
people raises an issue on the tracker and others implement and apply fixex.
--
Terry Jan Reedy
--
http://mail.python.org/mailman/listinfo/python-list
Re: How to get outer class name from an inner class?
On May 8, 1:05 pm, John Gordon gor...@panix.com wrote: I'm trying to come up with a scheme for organizing exceptions in my application. Currently, I'm using a base class which knows how to look up the text of a specific error in a database table, keyed on the error class name. The base class looks like this: class ApplicationException(Exception): Base class for application-specific errors. def get_message(self): Return the error message associated with this class name. class_name = self.__class__.__name__ return UserMessage.objects.get(key=class_name).text And then I define a bunch of subclasses which all have different names: class QuestionTooShortError(NetIDAppsError): User entered a security question which is too short. pass class QuestionTooLongError(NetIDAppsError): User entered a security question which is too long. pass This scheme works, but I'd like to make it more streamlined. Specifically, I'd like to group the classes underneath a parent class, like so: class Question(ApplicationException): class TooShort(ApplicationException): pass class TooLong(ApplicationException): pass This will make it easier in the future for organizing lots of sub-errors. My problem is this: the get_message() method in the base class only knows the current class name, i.e. TooShort or TooLong. But that's not enough; I also need to know the outer class name, i.e. Question.TooShort or Question.TooLong. How do I get the outer class name? This may be somewhat relevant to you, although it doesn't specifically answer your question for pre-3.3: http://www.python.org/dev/peps/pep-3155/ (Qualified name for classes and functions) -- http://mail.python.org/mailman/listinfo/python-list
