[Python-Dev] PEP-498: Literal String Formatting

Wes Turner wes.turner at gmail.com
Tue Aug 11 19:43:58 CEST 2015

On Tue, Aug 11, 2015 at 10:52 AM, Alexander Walters <tritium-list at sdamon.com
> wrote:

> On 8/11/2015 11:28, Wes Turner wrote:
> On Aug 11, 2015 10:19 AM, "Wes Turner" <wes.turner at gmail.com> wrote:
> - [ ] review all string interpolation (for "injection")
>   * [ ] review every '%'
>   * [ ] review every ".format()"
>   * [ ] review every f-string (AND LOCALS AND GLOBALS)
>   * every os.system, os.exec*, subprocess.Popen
>   * every unclosed tag
>   * every unescaped control character
> This would create work we don't need.
> Solution: __str_shell_ escapes, adds slashes, and quotes. __str__SQL__
> refs a global list of reserved words.
> I don't understand why % and .format got interjected into this.
> If you are mentioning them as 'get the unprocessed version of any string
> formatting', that is a bad idea, and not needed, since you already have an
> unprocessed string object.  Assuming the method were named "hypothetical":
> >>> 'foo bar'.hypothetical()      # returns 'foo bar'
> >>> '{0} bar'.format('foo').hypothetical()      # returns 'foo bar'
> >>> ('%s bar' % ('foo',)).hypothetical()     # returns 'foo bar'
> >>> f'{foo} bar'.hypothetical()     # returns '{foo} bar', prime for
> translation.
> could gettext not be modified to create the same AST as f'{foo} bar' when
> it is translated to '{foo} le bar.' and inject it back into the runtime?

well, we're talking about a functional [series of] transformations on
__str__ (or __unicode__); with globals and locals,
and more-or-less a macro for eliding this (**frequently wrong** because
when is a string not part of an output format with control characters that
need to be escaped before they're interpolated in).

% and str.format, (and gettext), are the current ways to do this,
and they are also **frequently wrong** because HTML, SQL.

The risk with this additional syntax is that unescaped globals and locals
are transcluded (and/or translated);
with an explicit (combination of) string prefixes to indicate
forwards-compatible functional composition
(of usually mutable types).
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