[Python-ideas] Dedicated string concatenation operator

[Ken Hilton]

Hi all, just another wild idea.

I've been working a lot with PHP lately (boo!), and one of the things I
have a love-hate relationship with in it is its string concatenation
operator: .
Counter-intuitively to Python, `.` is used to concatenate strings; `"str1"
. "str2"` evaluates to `"str1str2"`.
Even though it's kind of weird, I find the separation between addition and
concatenation useful. In PHP, `"str1" + "str2"` evaluates to 0; `"str1" .
"str2"` evaluates to `"str1str2"`. Obviously, in Python, `"str1" + "str2"`
could not evaluate to 0, it should instead raise a TypeError. But it's more
clear what is going on here:

    $content .= "foobar";
    $i += 1;

than here:

    content += "foobar"
    i += 1

I propose adding a dedicated operator for string concatenation. I don't
propose `.` as that operator - that would break too much. My initial idea
is to abuse the @ operator introduced for matrix multiplication to work for
string concatenation when applied to strings. This would be an example
result of that:

    >>> from numpy import matrix
    >>> matrix('1 2; 3 4') @ matrix('4 3; 2 1')
    [[ 8  5]
     [20 13]]
    >>> "str1" @ "str2"
    "str1str2"
    >>> "str1" @ 56 #str() is called on 56 before concatenating
    "str156"
    >>> 56 @ "str1" #str would also have __rmatmul__
    "56str1"
    >>> content = "foobar"
    >>> content @= "bazbang"
    >>> content @= "running out of ideas"
    >>> content
    'foobarbazbangrunning out of ideas'

However, the operator does not necessarily have to be @ - I merely picked
that because of its lack of use outside matrix math.

What are your thoughts?

Sincerely,
Ken Hilton;
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