Correct use of try,except and raise?

[Ben Finney]

ssecorp <circularfunc at gmail.com> writes:

> Is this correct use of exceptions? to raise an indexerror and add my
> own string insetad of just letting it raise a IndexError by itself
> and "blaming" it on list.pop?
> 
> class Stack(object):
>     def __init__(self, *items):
>         self.stack = list(items)

If you are passing a sequence conceptually, then it's more Pythonic to
pass it as a sequence explicitly::

    def __init__(self, items):
        """ Call with e.g. Stack(["foo", "bar"]) """
        self.stack = list(items)

>     def pop(self):
>         try:
>             return self.stack.pop()
>         except:
>             raise IndexError, "pop from empty stack"

Don't use this form of 'raise', it's deprecated. Instead, create the
exception instance with the arguments::

    raise IndexError("pop from empty stack")

Don't use a bare 'except'; you will thereby catch *all* exceptions in
the 'try' block, masking errors you did not expect to handle, making
debugging unnecessarily difficult. Instead, always be explicit about
*which* exceptions you're handling here.

Don't catch the exception only to raise a new one; the context of the
original exception is lost. If all you want to do is have a different
message, modify the existing exception instance's args and re-raise
it.

    try:
        return self.stack.pop()
    except IndexError, exc:
        exc.args = ["pop from empty stack"]
        raise

-- 
 \             “Experience is that marvelous thing that enables you to |
  `\   recognize a mistake when you make it again.” —Franklin P. Jones |
_o__)                                                                  |
Ben Finney