[Python-ideas] str.split with padding

Lie Ryan lie.1296 at gmail.com
Sat Mar 14 05:59:18 CET 2009

Steven D'Aprano wrote:
> On Sat, 14 Mar 2009 01:43:28 pm Lie Ryan wrote:
>> And Clover wrote:
>>> Here's a simple one I've reinvented in my own apps often enough
>>> that it might be worth adding to the built-in split() method:
>>>     s.split(sep[, maxsplit[, pad]])
>>> pad, if set True, would pad out the returned list with empty
>>> strings (strs/unicodes depending on returned datatype) so that the
>>> list was always (maxsplit+1) elements long. This allows one to do
>>> things like unpacking assignments:
>>>     user, hostname= address.split('@', 1, True)
>>> without having to worry about exceptions when the number of ‘sep’s
>>> in the string is unexpectedly fewer than ‘maxsplit’.
>> Can you find a better use case? For splitting email address, I think
>> I would want to know if the address turned out to be invalid (e.g. it
>> does not contain exactly 1 @s)
> What makes you think that email address must contain exactly one @ sign?
> Email being sent locally may contain zero @ signs, and email being sent 
> externally can contain one or more @ signs. Andy's code:
> user, hostname= address.split('@', 1, True)
> will fail on syntactically valid email addresses like this:
> fred(away @ the pub)@example.com

 From Wikipedia:
RFC invalid e-mail addresses
     * Abc.example.com (character @ is missing)
     * Abc. at example.com (character dot(.) is last in local part)
     * Abc..123 at example.com (character dot(.) is double)
     * A at b@c at example.com (only one @ is allowed outside quotations marks)
     * ()[]\;:,<>@example.com (none of the characters before the @ in 
this example, are allowed outside quotation marks)

Your example is valid email address if and only if it is enclosed in 
quotation mark: "fred(away @ the pub)"@example.com

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