On Wed, Nov 16, 2011 at 4:04 PM, Steven D'Aprano <st...@pearwood.info>wrote:
> Wayne Werner wrote:
>
>> <snip> It was explained to me once that in
>
> this case:
>>
>> "%s" % 42
>>
>> That since python expects to see a single-element tuple it treats it as or
>> converts 42 to a single element tuple.
>>
>
> "Treats as" may be true; "converts to" not so much. What it actually does
> is this:
>
> py> import dis
> py> dis.dis(compile('"%s" % x', '', 'single'))
> 1 0 LOAD_CONST 0 ('%s')
> 3 LOAD_NAME 0 (x)
> 6 BINARY_MODULO
> 7 PRINT_EXPR
> 8 LOAD_CONST 1 (None)
> 11 RETURN_VALUE
>
>
> Notice that the call to BINARY_MODULO (the % operator) takes two
> arguments, the string "%s" and the object x, whatever it happens to be.
> Python can't convert x to a tuple at this point, because it doesn't know
> what x is, and it may not know how many format specifiers are in the string
> either.
>
> Once the string and the object hit BINARY_MODULO, all bets are off. It
> will do whatever it likes, because that's purely internal implementation.
Ah, very cool. Just because I was interested, I did the same thing, only
using (x,) and there was only one difference (line? 6):
>>> dis.dis(compile('"%s" % (x, )', '', 'single'))
1 0 LOAD_CONST 0 ('%s')
3 LOAD_NAME 0 (x)
6 BUILD_TUPLE 1
9 BINARY_MODULO
10 PRINT_EXPR
11 LOAD_CONST 1 (None)
14 RETURN_VALUE
<PSA tune>
The more you know!
Thanks,
-Wayne
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