new string function suggestion

[Andy]

What do people think of this?

'prefixed string'.lchop('prefix') == 'ed string'
'string with suffix'.rchop('suffix') == 'string with '
'prefix and suffix.chop('prefix', 'suffix') == ' and '

The names are analogous to strip, rstrip, and lstrip.  But the functionality 
is basically this:

def lchop(self, prefix):
  assert self.startswith(prefix)
  return self[len(prefix):]

def rchop(self, suffix):
  assert self.endswith(suffix)
  return self[:-len(suffix]

def chop(self, prefix, suffix):
  assert self.startswith(prefix)
  assert self.endswith(suffix)
  return self[len(prefix):-len(suffix]

The assert can be a raise of an appropriate exception instead.  I find this 
to be a very common need, and often newbies assume that the 
strip/lstrip/rstrip family behaves like this, but of course they don't.

I get tired of writing stuff like:

if path.startswith('html/'):
  path = path[len('html/'):]
elif s.startswith('text/'):
  path = path[len('text/'):]

It just gets tedious, and there is duplication.  Instead I could just write:

try:
  path = path.lchop('html/')
  path = path.lchop('text/')
except SomeException:
  pass

Does anyone else find this to be a common need?  Has this been suggested 
before?

Andy