Forcing quote characters in repr(STRING), how?

[François Pinard]

Hi!  Cleaning old mail, I stumbled on that old conversation:

---------------------------------------------------------------------->
[François Pinard]

> When using `repr()' on a string, Python automatically selects if it
> will use single or double quotes to enclose the produced representation
> of the string.  Is there a clean way to force that choice to be, under
> user control, a particular quote character (either simple or double)?

[Tim Peters]

> Not a clean way, nor even a dirty way:  the logic is hardcoded.

[Duncan Booth]

> Never say there isn't a dirty way.  The following works, although I
> really wouldn't recommend it: [...]

> def quote(s, dquote=0):
>     """Return repr of the string argument forcing single or double 
> quotes."""
>     if dquote:
>         nasty="'\0"
>     else:
>         nasty='"\0'
>     r = repr(nasty+s)
>     bad = len(`nasty`)-1
>     r = r[0]+r[bad:]
>     return r

> if __name__=='__main__':
>     def test(s):
>         print "single quote(%s) -> %s" % (`s`, quote(s, 0))
>         print "double quote(%s) -> %s" % (`s`, quote(s, 1))
>     test("ab'cd")
>     test("ab'c\"d")
>     test('ab"cd')
----------------------------------------------------------------------<

Despite not recommended, I nevertheless followed the trick above in Pymacs.
Preceded by a long comment, the little piece of code looks almost clean :-).

    [...]
    elif type(value) == types.StringType:
        # Python delimits a string it by single quotes preferably, unless
        # single quotes appear within the string while double quotes do
        # not, in which case it uses double quotes for string delimiters.
        # Checking the string contents, the C code stops at the first NUL.
        # We prefix the string with a single quote and a NUL, this forces
        # double quotes as delimiters for the whole prefixed string.  Then,
        # we get rid of the representation of the single quote and the NUL.
        write('"' + repr("'\0" + value)[6:])
    [...]

-- 
François Pinard   http://www.iro.umontreal.ca/~pinard