[Python-Dev] PEP 3101 Update

[Edward Loper]

Steven Bethard wrote:
> On 5/7/06, Edward Loper <edloper at gradient.cis.upenn.edu> wrote:
>> Talin wrote:
>>>      Braces can be escaped using a backslash:
>>>
>>>          "My name is {0} :-\{\}".format('Fred')
>>>
>>>      Which would produce:
>>>
>>>          "My name is Fred :-{}"
>> Do backslashes also need to be backslashed then?  If not, then what is
>> the translation of this:?
>>
>>      r'abc\{%s\}' % 'x'
> 
> I believe the proposal is taking advantage of the fact that '\{' is
> not interpreted as an escape sequence -- it is interpreted as a
> literal backslash followed by an open brace:

Yes, I knew that fact, but it's not related to my question.  The basic 
issue is, that if you have a quote character ('\\'), then you usually 
need to be able to quote that quote character ('\\\\') in at least some 
contexts.

So I'll try again with a different example.  I'll avoid using raw 
strings, just because doing so seems to have confused a couple people 
about what my question is about.  Let's say I have a program now that 
contains the following line:

   print 'Foo\\%s' % x

And I'd like to translate that to use str.format.  How do I do it?  If I 
just replace %s with {0} then I get:

   print 'Foo\\{0}'.format(x)

but this will presumably raise an exception, since the '\\{' (which is 
identical to '\{') gets treated as a quoted brace, and the '}' is 
unmatched.  If it were possible to backslash backslashes, then I could do:

   print 'Foo\\\\{1}' % x

(which can also be spelled r'Foo\\{1}' -- i.e., the string now contains 
two backslash characters).

But I haven't seen any mention of backslashing backslashes so far.

-Edward