Alternative dictionary output format?

[rael at my-deja.com]

I would like to be able to take a string which contains C-format
extension variables (e.g., "%(foo)s") and format it with a dictionary in
the standard way, except I would like the format to only substitute for
the recognized variables and to ignore other instances of percent signs.

For example, given this program:

s = "%(href)s/foo/bar?x=%m&y=%n"
d = {'href': "http://www.gomer.com"}
u = s % d
print s

running it produces:

% python t.py
Traceback (innermost last):
  File "t.py", line 3, in ?
    u = s % d
TypeError: not enough arguments for format string

And this program:

s = "%m foobar %(href)s/foo/bar?x=%m&y=%n"
d = {'href': "http://www.gomer.com"}
u = s % d
print s

produces:

% python t.py
Traceback (innermost last):
  File "t.py", line 3, in ?
    u = s % d
ValueError: unsupported format character 'm' (0x6d)

What I would like to write:

s = "%m foobar %(href)s/foo/bar?x=%m&y=%n"
d = {'href': "http://www.gomer.com"}
u = format_ignoring_non_variable_percent_signs(s, d)
print s

And what I would like the behavior to be:

% python t.py
%m foobar http://www.gomer.com/foo/bar?x=%m&y=%n

Is there any way to surface the C interface for the '%' format operator
and to allow an option to effectively wrap each format attempt with a
try/except/pass block?

I realize there are other ways to do this (regular expression
substitution, write my own C extension, etc.), but formatting a string
with multiple variables using a dictionary and the format operator is
extremely convenient (and I imagine relatively effiecient), and I
thought others may have come across this as well.


Bill
--
r a e l @
d e j a .
c o m


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