[Python-ideas] String interpolation again. (original) (raw)

Mike Meyer mwm-keyword-python.b4bdba at mired.org
Fri Jul 23 15:37:05 CEST 2010

On Fri, 23 Jul 2010 15:25:42 +0200 Masklinn <masklinn at masklinn.net> wrote:

On 2010-07-23, at 15:05 , Mike Meyer wrote: > The first problem with this kind of thing is that there's no obvious > reason why 12 + '34' should be '1234' instead of 46. > > Java variables have declared types. This means the above situation can > be detected at compile time, and the implicit conversion added > then. In Python, you have to do the tests at run time, which will slow > everything down. Actually, it's much simpler than that for Java: the + operator is specially overloaded any time a string is involved to become a "convert and concatenate" operator similar to PHP's "." rather than the usual "add" operator.

In Python, the equivalent behavior would be to special case the addition operator so that it checks if either operand is a string and if it is convert and concatenate the other one, otherwise apply normal resolution.

I would hope the Java version isn't as convoluted as you say (but given Java, it may be): all this really requires is that the string version of + include the conversion. In python, that would be making str.add (and friends) do the conversion. Given that in Python, str(a_string) is a_string, and doing the type check on a string (via either type or isinstance) is about the same speed as calling str on it (just under .2 usecs/loop), you might as well just always do the conversion. Or maybe this breaks unicode...

Assuming, of course, you actually think this is a good idea.

<mike

-- Mike Meyer <mwm at mired.org> http://www.mired.org/consulting.html Independent Network/Unix/Perforce consultant, email for more information.

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