On Tue, 13 Nov 2012 10:08:59 -0500, Colin J. Williams wrote:
> Is there some way to get more informative error messages from the
> builtin format?
Yes -- post a feature request on the Python bug tracker, then wait until
Python 3.4 comes out in about 16 months.
:(
> Most messages are such as:
> Traceback (most recent call last):
> File "<interactive input>", line 1, in <module>
> ValueError: Invalid conversion specification
>
> This example doesn't point to the first invalid case.
Better error messages would be valuable.
> [Dbg]>>> format((25, 31),'{0^9o} a(1:9x}')
> Traceback (most recent call last):
> File "<interactive input>", line 1, in <module>
> ValueError: Invalid conversion specification
I see at least three problems.
(1) The first brace substitution is missing the colon between the
argument selector "0" and the format spec "^9o": should be "{0:^9o}".
(2) The second format string has an opening round bracket instead of
brace: (1:9x}
(3) But you are confusing the str.format method with the format function.
The format function doesn't take brace substitutions!
The string format method takes a template including brace substitutions,
plus multiple "objects to be substituted", like this:
py> '{0:^9o} a{1:9x}'.format(25, 31)
' 31 a 1f'
In this case, the template '{0:^9o} a{1:9x}' requires two arguments since
it has two substitutions, {0} and {1}. Each substitution has a format
spec following the colon: {0:^9o} and {1:9x}
But the format function only takes a single "object to be substituted",
and so doesn't take a brace substitution. Instead, it just takes the
format spec part:
py> format(25, '^9o')
' 31 '
py> format(31, '^9o')
' 37 '
format will not split a tuple into multiple arguments for you, since the
tuple is considered a single object.
--
Steven
--
http://mail.python.org/mailman/listinfo/python-list
