[Tutor] Question regarding syntax

John Morris jrmorrisnc at gmail.com
Wed Jul 11 18:31:36 CEST 2007

On 7/11/07, Dave Kuhlman <dkuhlman at rexx.com> wrote:
> On Wed, Jul 11, 2007 at 11:03:18AM -0400, John Morris wrote:
> > I'm editing some code from Mailman and seeing:
> >
> > legend = _("%(hostname)s Mailing Lists")
> >
> The outer parentheses are a function call.  The underscore
> is a name that has a callable as a value, I suppose.  I
> believe that the value of the name underscore is the last
> expression evaluated, but I'm not sure.

Right... Thanks, I figured it was something like that but it was not
something I'd encountered.
so if _ =  foo
bar = _("test") is equivalent to
bar = foo("test")

Mailman is a great product.  But that bit of code is not, I think,
> very good code.  In Python explicitness is a virtue, and the use of
> the underscore is implicit and is not very Pythonic.

Agreed. The _ stuff is reminiscent of Perl  $_, @_ and friends. I'd go miles
personally to
avoid that usage, personally.

I have done the whole 'import this' and mightily strive to grok it all
properly on a regular basis. ;-)

By the way, The inner parentheses are a formatting operation.
> %(x)s will be replaced by the value of x in Example:
>    vals = {'animal': 'dog'}
>    "Rover is a big %(animal)s." % vals
> "%(animal)s" will be replaced by "dog".  When you use this form,
> the value on the right of the formatting operator must be a
> dictionary.  More from the library reference:
>     When the right argument is a dictionary (or other mapping type),
>     then the formats in the string must include a parenthesised mapping
>     key into that dictionary inserted immediately after the "%"
>     character. The mapping key selects the value to be formatted from
>     the mapping. For example:
>     >>> print '%(language)s has %(#)03d quote types.' % \
>               {'language': "Python", "#": 2}
>     Python has 002 quote types.
>           -- http://docs.python.org/lib/typesseq-strings.html

Thanks for this too, though it's more completeness than I needed (just
wondered if _( was "special" usage or what. Kudos on an excellent reply.

So, any really good tutorials on FP and map, filter, zip, lambda ?
I'm trying to wrap my mind around those better...

Thanks much!
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