Path: csiph.com!fu-berlin.de!uni-berlin.de!not-for-mail
From: Stephen Hansen <me+python@ixokai.io>
Newsgroups: comp.lang.python
Subject: Re: one-element tuples
Date: Sun, 10 Apr 2016 18:07:46 -0700
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On Sun, Apr 10, 2016, at 05:48 PM, Fillmore wrote:
> On 04/10/2016 08:31 PM, Ben Finney wrote:
> > Can you describe explicitly what that =E2=80=9Cdiscontinuation point=E2=
=80=9D is? I'm
> > not seeing it.
>=20
> Here you go:
>=20
>  >>> a =3D '"string1"'

Here, "a" is a string that contains a double quoted string. So if you
evaluate it, you get a string.

>  >>> b =3D '"string1","string2"'

Here, "b" is a string that contains two double quoted strings separated
by a comma. So if you evaluate it, you get a tuple of two strings.

>  >>> c =3D '"string1","string2","string3"'

This is as above, but with three items.

With that in mind:
>  >>> ea =3D eval(a)
>  >>> eb =3D eval(b)
>  >>> ec =3D eval(c)
>  >>> type(ea)
> <class 'str'>=20
>  >>> type(eb)
> <class 'tuple'>
>  >>> type(ec)
> <class 'tuple'>

This should all be expected. The commas, when you evaluate them, are in
B&C making tuples. There's only a single string in A, so you get a
string. If you wanted a one item tuple, you would have written:

>>> a =3D '"string1",'

Note the trailing comma.

> I can tell you that it exists because it bit me in the butt today...
>=20
> and mind you, I am not saying that this is wrong. I'm just saying that it
> surprised me.

If the above doesn't explain it, then I still don't understand what
you're finding surprising and what you'd expect otherwise.

---Stephen
m e @ i x o k a i . i o