How does the python regex [^@]+@[^@]+\.[^@]+ work in checking emails?

Question

(from Python check for valid email address?)

I don't completely understand

[^@]+@[^@]+\.[^@]+

Can someone explain this in detail?

Type in your regex at http://rick.measham.id.au/paste/explain.pl and see for yourself. Voting to close. — devnull, Apr 17 '14 at 02:03
This answer from the [Stack Overflow Regular Expressions FAQ](http://stackoverflow.com/a/22944075/2736496) may also be of interest: [validating email addresses](http://stackoverflow.com/questions/201323/using-a-regular-expression-to-validate-an-email-address) as listed under "Common Validation Tasks] — aliteralmind, Apr 17 '14 at 02:11

score 2 · Accepted Answer · answered Apr 17 '14 at 02:05

It looks for 1+ non-@ characters, followed by an @, followed by 1+ non-@ characters, followed by a ., followed by 1+ non-@ characters.

[]s denote a character class, and the ^ negates the character class. + matches 1+ of the preceding characters. Finally, the . is escaped like \. because the . is a reserved symbol meaning "any character".

This means it isn't the best method for checking emails, since there are a lot more restrictions. For example, this would validate a 10,000 character long email or an email with a domain like !@#.com.

Get used to using a tool like Regex101 for testing expressions and getting good descriptions.

score 0 · Answer 2 · answered Apr 17 '14 at 02:06

[^@]+ - checks for anything that is not the @ symbol, one or more times.

@ searches for the @ symbol, clearly.

\. searches for the . character (it must be escaped since . searches for any character)

So it looks for any string not containing @, followed by @, followed by any string not containing @, followed by ., followed by any string not containing @.

score 0 · Answer 3 · edited May 23 '17 at 12:20

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A proper validator for the RFC822 address specification (section "6. ADDRESS SPECIFICATION" on page 27) is a bit more complex than a small regex.

In order to do this properly, a grammar would be needed(like the one described in said rfc) but a regex works too. Such a regex can be found in the Email::Valid module, more exactly right here. I haven't tried that regex in Python(but it works fine in Perl).

AFAIK that's the de facto way of checking if an e-mail address is rfc822-valid. Also see this SO post for more details.

But to answer your question now, the regex [^@]+@[^@]+\.[^@]+ reads as "At least one or more non-@ , then a @ , then at least one or more non-@ , then a dot, then at least one or more non-@".

edited May 23 '17 at 12:20

Community

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answered Apr 17 '14 at 02:23

wsdookadr

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The de facto way of determining if an e-mail address is valid is *sending an e-mail*. If it bounces or the mailer reports an error, it's invalid. – ashastral Apr 17 '14 at 02:27
I think there's a misunderstanding, I meant valid as in rfc822-valid (as can be read above^^) – wsdookadr Apr 17 '14 at 02:29
Yes, that's a more accurate way to word it. – ashastral Apr 17 '14 at 02:34

How does the python regex [^@]+@[^@]+\.[^@]+ work in checking emails?

3 Answers3