Your testing example was good, and similarly, it also aids in debugging down
the line. For example, if you have a method that opens a file and
manipulates the data, its generally a good idea to know if an exception
coming out of that method is related to the file ops or due to some use of
the standard library, or from a defined bad operation from your code (error
condition). Defining a derived exception class is a bit safer for client
code to handle, rather than just parsing the exception message.
It is also convenient to define your own exception, even without any
extra information besides the message, if you need to raise it in
several places. In the very least it removes the message duplication
and facilitates in debugging.
When is it a good idea to subclass and create my own error
class?
Your testing example was good, and similarly, it also aids in
debugging down
the line. For example, if you have a method that opens a file and
manipulates the data, its generally a good idea to know if an exception
coming out of that method is related to the file ops or due to some
use of
the standard library, or from a defined bad operation from your code
(error
condition). Defining a derived exception class is a bit safer for
client
code to handle, rather than just parsing the exception message.
When is it a good idea to subclass and create my own error
class?
Your testing example was good, and similarly, it also aids in debugging
down
the line. For example, if you have a method that opens a file and
manipulates the data, its generally a good idea to know if an exception
coming out of that method is related to the file ops or due to some use
of
the standard library, or from a defined bad operation from your code
(error
condition). Defining a derived exception class is a bit safer for client
code to handle, rather than just parsing the exception message.
Not only is it “a bit safer” but it’s much cleaner (and maybe faster,
too). Relying on the exception type is better, because it makes handling
of those exceptions easier (especially if they need to be dealt with at
different levels of the application). And just think about
internationalized error messages…