On 14/08/2019 14:19:05, Marat Sharafutdinov wrote:
While using any library there is a need to handle exceptions it raises. In
ideal conditions author of library defines base exception and builds hierarchy
of exceptions based on it. Moreover, all exceptions a library raises (including
those that do not inherit its base exception) are documented and this
information is kept up to date. Unfortunately, this is not always the case.
Library authors are free to use the language exception mechanism in any way. So
instead of using documented features of library as a black box, the user often
has to plunge into the source code of a library itself and look for exceptions
it could raise in order to be prepared for them.
The essence of my idea is simple and does not affects compatibility with existing code:
to automatically define a magic attribute of module under the working name
"__exception__" while importing any module. It can be used in usual way, for
example:
try:
.. any_module.anything
.. except any_module.__ exception__:
.. ...
Here any exception an author of library raises can be handled. This way you can
handle any exception that occurs in the library without even knowing what
exceptions it can raise.
The important point is that only exceptions raised in library itself are
handled. Those exceptions that can be raised in underlying libraries and so on
through the dependency chain should be handled separately.
Developing this idea, it could be more universal mechanism that works not only
with modules, but with any objects of the language. For instance:
try:
.. any_function()
.. except any_function.__ exception__:
.. ...
or
try:
.. AnyClass.anything
.. except AnyClass.__ exception__:
.. ...
It is important to understand the key difference between this mechanism and the
capture of broad exception: only those exceptions are handled that are RAISED
EXPLICITLY inside the object, while broad exception captures ANY exceptions
that may occur in the object.
Sticking to modules for the moment: I'm not completely sure (despite
the above sentence) whether you mean exceptions *raised* in a module, or
exceptions *defined* (and raised) in a module.
What if a module says e.g.
raise ValueError
would that trapped by
except any_module.__ exception__:
? Please clarify.
Best wishes
Rob Cliffe
It seems to me this idea will help library users more correctly handle their
exceptions if this is problematic. This will save time and make code more
reliable.
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