Which method to check if string index is queal to character.

[Chris Angelico]

On Tue, Dec 29, 2020 at 10:08 AM Avi Gross via Python-list
<python-list at python.org> wrote:
>
> This may be a nit, but can we agree all valid email addresses as used today
> have more than an @ symbol?
>
> I see it as requiring at least one character before the @ that come from a
> list of allowed characters (perhaps not ASCII) but does not include the
> symbol @ again. It is normally followed by some minimal number of characters
> and maybe  a period and one of the currently valid domains like .com or .it
> but the latter gets tricky as it can look like user at abd.def.att.com or other
> long variations where only the final component must be testable in the
> program.

There can be an @ in the first part of the address, and the domain may
well not have a dot.

> The lack of an at-sign suggests it is not an email address. The lack of
> anything before or after also seems to disqualify it. You may be able to add
> more conditions but as noted, having more than one at-sign may also
> disqualify it.

Lack of an at sign means it's a local address that can't be routed
over the internet, and in many contexts, it's reasonable to exclude
those. But two isn't illegal.

> I am sure someone has some complex regular expressions that they think
> matches only potentially valid strings but, of course, as noted by Chris, to
> really validate that an address works might require sending something and
> validating a human replied and that can be quite  task.
>

Yes, many such regexes exist, and they are *all wrong*. Without
exception. I don't think it's actually possible for a regex to
perfectly match all (syntactically) valid email addresses and nothing
else.

ChrisA