[Python-ideas] Re: New explicit methods to trim strings

7 Mar 2020

      On 07Mar2020 15:31, Alex Hall <alex.mojaki@gmail.com> wrote:
...
I've defined functions like this in my own utility library and I use them
all the time, so I think they're very useful and would like to seem them
built in. But I have two functions for each end:
def strip_optional_suffix(string, suffix):
   """
...
...
...
strip_optional_suffix('abcdef', 'def')
   'abc'
strip_optional_suffix('abcdef', '123')
   'abcdef'
   """
   if string.endswith(suffix):
       return string[:-len(suffix)]
   return string
My utility library has them too, like this:

    def cutprefix(s, prefix):
      ''' Strip a `prefix` from the front of `s`.
          Return the suffix if `.startswith(prefix)`, else `s`.

          Example:

              >>> abc_def = 'abc.def'
              >>> cutprefix(abc_def, 'abc.')
              'def'
              >>> cutprefix(abc_def, 'zzz.')
              'abc.def'
              >>> cutprefix(abc_def, '.zzz') is abc_def
              True
      '''
      if prefix and s.startswith(prefix):
        return s[len(prefix):]
      return s

    def cutsuffix(s, suffix):
      ''' Strip a `suffix` from the end of `s`.
          Return the prefix if `.endswith(suffix)`, else `s`.

          Example:

              >>> abc_def = 'abc.def'
              >>> cutsuffix(abc_def, '.def')
              'abc'
              >>> cutsuffix(abc_def, '.zzz')
              'abc.def'
              >>> cutsuffix(abc_def, '.zzz') is abc_def
              True
      '''
      if suffix and s.endswith(suffix):
        return s[:-len(suffix)]
      return s

Like yours, they return the original object if unchanged. I think yours 
misbehaved if given an empty suffix, which mine special cases out:

    >>> 'abc'[:-0]
    ''

Cheers,
Cameron Simpson <cs@cskk.id.au>