[Python-ideas] Re: Different exceptions for assert

David, It seems I didn't state clearly enough my original statement, which is that software will *_always_ *fail, even because of faulty hardware components, or cosmic rays. For software to be resilient, it must assert it's expected state. But that doesn't have to be with the *assert* statement, perhaps less so when the Python tradition is that those go away with just a "-O". I won't vouch for an *"invariant"* statement, because that's probably too much to ask for. So I'll just use *"if"* to assert more invariants in the code I write. Cheers, On Sat, Sep 11, 2021 at 2:05 PM David Mertz, Ph.D. wrote:

On Sat, Sep 11, 2021 at 9:20 AM Juancarlo Añez wrote:

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I'm happy about dropping the DBC theme and rebooting to make *assert* easier to use so it gets used more.

I agree with Steven, Marc-Andé, and others in seeing "using assertions more" as an anti-goal.

This isn't to say that a given program should have fewer—nor more—lines that start with `assert`. Rather, assertions should be use to ASSERT conditions that should NEVER be violated. They are NOT to check whether user input is bad. Nor whether a disk is unreliable. Nor whether a computation takes too long. Nor whether a value is outside of a useful range. Nor any of the other things that regular exception handling is well designed for.

If for some reason you find yourself completely unable to write "if not (condition_to_check): ..." for mysterious reasons, you could use assert this way (but don't):

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try: ... assert 2+2==5, "Bad arithmetic" ... except AssertionError: ... print("Configuring stuff to log problem") ... raise ... Configuring stuff to log problem Traceback (most recent call last): File "<ipython-input-3-2a9bdbc65744>", line 2, in <module> assert 2+2 == 5, "Bad arithmetic" AssertionError: Bad arithmetic

But again, that's bad code for the same reason your proposal would be bad code. Assertions have the entire purpose of being possible to disable, and to express conditions a programmer believes are *necessarily true*.

-- Keeping medicines from the bloodstreams of the sick; food from the bellies of the hungry; books from the hands of the uneducated; technology from the underdeveloped; and putting advocates of freedom in prisons. Intellectual property is to the 21st century what the slave trade was to the 16th.

-- Juancarlo *Añez*