format sring question

[Lowell Kirsh]

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?

Lowell

[Andrew Dalke]

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
da***@dalkescie ntific.com

[Peter Otten]

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?

Lowell

The only difference is that the _second_ one will work for non-strings, too,
when only the 'format' argument is passed and str(format) does not contain
any '%' characters. Two consecutive '%' are always converted into one, I'd
say this is broken behaviour when the conversion is applied on the result
of str(format) and format is not a string.

IMHO the second form is extremely bad code and you better forget about it
fast.

Peter

[Lowell Kirsh]

thanks to both of you. bye bye second version.

Lowell

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?

Lowell