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Re: asyncio: What is the difference between tasks, futures, and coroutines?

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On Fri, May 8, 2015 at 9:53 PM, Dave Angel <davea@davea.name> wrote:
> One thing newbies get tripped up by is having some path through their code
> that doesn't explicitly return.  And in Python that path therefore returns
> None.  It's most commonly confusing when there are nested ifs, and one of
> the "inner ifs" doesn't have an else clause.
>
> Anyway, it's marginally more useful to that newbie if the compiler would
> produce an error instead of later seeing a runtime error due to an
> unexpected None result.
>
> I don't think Python would be improved by detecting such a condition and
> reporting on it.  That's a job for a linter, or a style guide program.

They're not hard for linters to notice. After all, there's a clear
difference of intent between "return" (or just falling off the end of
the function) and "return None", even though they compile to the same
byte code. Though if you start enforcing that in your checkin policy,
you might have to deal with this kind of thing:

def raise_with_code(code):
    raise SpamError("Error %d in spamination: %s" % (code,
errortext.get(code, "<unknown>")))

def spaminate_text(f):
    rc = low_level_spamination_function(f)
    if not rc: return low_level_get_spamination_result()
    raise_with_code(rc)

Clearly one branch returns a value... but figuring out that the other
one always raises isn't easy. (Though I suppose in this case it could
be dealt with by having a function that constructs the error, and then
you "raise make_spam_error(rc)" instead.)

You're definitely right that Python shouldn't check for it.

ChrisA

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asyncio: What is the difference between tasks, futures, and coroutines? Paul  Moore <p.f.moore@gmail.com> - 2015-05-05 08:22 -0700
  Re: asyncio: What is the difference between tasks, futures, and coroutines? Zachary Ware <zachary.ware+pylist@gmail.com> - 2015-05-05 11:11 -0500
    Re: asyncio: What is the difference between tasks, futures, and coroutines? Paul  Moore <p.f.moore@gmail.com> - 2015-05-05 10:55 -0700
  Re: asyncio: What is the difference between tasks, futures, and coroutines? Terry Reedy <tjreedy@udel.edu> - 2015-05-05 13:15 -0400
  Re: asyncio: What is the difference between tasks, futures, and coroutines? Marko Rauhamaa <marko@pacujo.net> - 2015-05-05 20:45 +0300
    Re: asyncio: What is the difference between tasks, futures, and coroutines? Rustom Mody <rustompmody@gmail.com> - 2015-05-05 21:47 -0700
      Re: asyncio: What is the difference between tasks, futures, and coroutines? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-06 15:48 +1000
        Re: asyncio: What is the difference between tasks, futures, and coroutines? Rustom Mody <rustompmody@gmail.com> - 2015-05-07 21:06 -0700
          Re: asyncio: What is the difference between tasks, futures, and coroutines? Chris Angelico <rosuav@gmail.com> - 2015-05-08 14:33 +1000
            Re: asyncio: What is the difference between tasks, futures, and coroutines? Rustom Mody <rustompmody@gmail.com> - 2015-05-07 21:53 -0700
              Re: asyncio: What is the difference between tasks, futures, and coroutines? Rustom Mody <rustompmody@gmail.com> - 2015-05-07 21:55 -0700
              Re: asyncio: What is the difference between tasks, futures, and coroutines? Chris Angelico <rosuav@gmail.com> - 2015-05-08 15:09 +1000
                Re: asyncio: What is the difference between tasks, futures, and coroutines? Rustom Mody <rustompmody@gmail.com> - 2015-05-07 23:36 -0700
                Re: asyncio: What is the difference between tasks, futures, and coroutines? Chris Angelico <rosuav@gmail.com> - 2015-05-08 16:42 +1000
                Re: asyncio: What is the difference between tasks, futures, and coroutines? Dave Angel <davea@davea.name> - 2015-05-08 07:53 -0400
                Re: asyncio: What is the difference between tasks, futures, and coroutines? Chris Angelico <rosuav@gmail.com> - 2015-05-08 23:02 +1000
      Re: asyncio: What is the difference between tasks, futures, and coroutines? Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2015-05-06 09:11 -0400
        Re: asyncio: What is the difference between tasks, futures, and coroutines? Rustom Mody <rustompmody@gmail.com> - 2015-05-07 21:20 -0700
  Re: asyncio: What is the difference between tasks, futures, and coroutines? Ian Kelly <ian.g.kelly@gmail.com> - 2015-05-05 11:46 -0600
    Re: asyncio: What is the difference between tasks, futures, and coroutines? Paul  Moore <p.f.moore@gmail.com> - 2015-05-05 11:03 -0700
  Re: asyncio: What is the difference between tasks, futures, and coroutines? Skip Montanaro <skip.montanaro@gmail.com> - 2015-05-05 12:55 -0500
  Re: asyncio: What is the difference between tasks, futures, and coroutines? Terry Reedy <tjreedy@udel.edu> - 2015-05-05 18:38 -0400

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