[Python-ideas] adding a trim convenience function

[Tal Einat]

Tal Einat wrote:
> Erick Tryzelaar wrote:
>  > I find that when I'm normalizing strings, I end up writing this a lot:
>  >
>  >  sites = ['www.google.com', 'http://python.org', 'www.yahoo.com']
>  >  new_sites = []
>  >  for site in sites:
>  >   if site.startswith('http://'):
>  >     site = site[len('http://'):]
>  >   new_sites.append(site)
>  >
>  >  But it'd be much nicer if I could use a convenience function trim that
>  >  would do this for me, so I could just use a comprehension:
>  >
>  >  def ltrim(s, prefix):
>  >   if s.startswith(prefix):
>  >     return s[len(prefix):]
>  >   return s
>  >
>  >  sites = ['www.google.com', 'http://python.org', 'www.yahoo.com']
>  >  sites = [ltrim(site, 'http://') for site in sites]
>  >
>  >  Would there be any interest to add this helper function, as well as an
>  >  "rtrim" and "trim", to the str class?
>  >
>
>  I'm against adding this as a string method, or even a a function in the stdlib.
>
>  I've done a lot of text processing with Python and have hardly ever
>  needed something like this. If you think this would be useful often, a
>  good way to convince this list is to show some examples of how it
>  could improve code in the standard library, noting how common they
>  are.
>
>  In general, having a lot of string methods is very harmful because it
>  makes learning Python a longer and more confusing process.
>  Furthermore, this functionality is very simple and easy to implement,
>  I just thought of 3 different ways [1] to implement this function in a
>  simple, readable one-liner. For these reasons, unless you can show
>  that this will be very useful very often, I'm against.
>
>  - Tal
>
>
>  [1]
>  ltrim = lambda item, to_trim,: re.sub('^' + to_trim, '', item)
>  ltrim = lambda item, x: item[0 if not item.startswith(x) else len(x):]
>  ltrim = lambda item, to_trim: ''.join(item.split(to_trim, 1))
>

Ignore the third implementation, it's broken... here's another one in its place:
ltrim = lambda item, x: item[item.startswith(x) * len(x):]

- Tal