String formatting with the format string syntax

Miki miki.tebeka at gmail.com
Tue Sep 14 20:20:18 CEST 2010


You can use ** syntax:
>>> english = {'hello':'hello'}
>>> s.format(**english)

On Sep 14, 9:59 am, Andre Alexander Bell <p... at andre-bell.de> wrote:
> Hello,
>
> I'm used to write in Python something like
>
>  >>> s = 'some text that says: %(hello)s'
>
> and then have a dictionary like
>
>  >>> english = { 'hello': 'hello' }
>
> and get the formatted output like this:
>
>  >>> s % english
>
> Occasionally I want to extract the field names from the template string.
> I was used to write a class like
>
> class Extractor(object):
>      def __init__(self):
>          self.keys = []
>      def __getitem__(self, key):
>          self.keys.append(key)
>          return ''
>
> and use it like this:
>
>  >>> e = Extractor()
>  >>> res = s % e
>  >>> e.keys
> ['hello']
>
> Now Python has the format method for string formatting with the more
> advanced handling. So I could as well write
>
>  >>> s = 'some text that says: {hello!s}'
>  >>> s.format(hello='hello')
>
> My question is, if I do have a string template which uses the newer
> format string syntax, how do I best extract the field information?
>
> I found the str._formatter_parser() method which I could use like this:
>
> keys = []
> for (a, key, c, d) in s._formatter_parser():
>      if key:
>          keys.append(key)
>
> Is there a more elegant solution?
> What are a, c, d?
> Where can I find additional information on this method?
> Should one use a method that actually starts with an _?
> Couldn't this one change any time soon?
>
> Thanks for any help
>
> Andre




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