format sring question
Andrew Dalke
adalke at mindspring.com
Fri Sep 3 04:07:06 EDT 2004
Lowell Kirsh wrote:
> In Peter Norvig's Infrequently Answered Questions he explains that the
> following 2 fnctions look almost identical but are not the same:
>
> def printf(format, *args): print format % args,
>
> def printf(format, *args): print str(format) % args,
>
> The only difference is that in the second one, str(format) replaces
> format. If args are not given and the format string contains a '%', the
> first will work but the second will not. Why is this so? It seems to me
> like '100%' and str('100%) are the same object, no?
The both fail the same way for me; I can't reproduce
a difference.
>>> def printf1(format, *args): print format % args,
...
>>> def printf2(format, *args): print str(format) % args,
...
>>> printf1("100%")
Traceback (most recent call last):
File "<stdin>", line 1, in ?
File "<stdin>", line 1, in printf1
ValueError: incomplete format
>>> printf2("100%")
Traceback (most recent call last):
File "<stdin>", line 1, in ?
File "<stdin>", line 1, in printf2
ValueError: incomplete format
>>>
>>> printf1("100%%")
100%
>>> printf2("100%%")
100%
>>>
My guess is there's supposed to be some sort of
confusing between the trailing ',' when used in a
print statement, to suppress the trailing newline,
and when used to indicate a tuple, as in
a = args,
to create a single element tuple. In that case,
% args, might be a single element tuple where the
first element is the tuple of args.
Andrew
dalke at dalkescientific.com
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