#39939 introduced .removeprefix for several classes. I propose adding kwargs-only parameter `, *, strict: bool = False`. It should raise some exception (I'm unuse what exactly) if the string DOES NOT start from specified prefix. False by default only for compatibility purposes. Personally I think it should be True, but I understand why it's impossible to change API.

The same about `removesuffix()`.

ValueError would seem to be the right exception to use.

If this parameter were to be added (I'm not convinced that it should be), I'd prefer to call it something more specific than "strict", since "strict" can mean lots of things.

@Jelle Zijlstra, they did think about this in the pep; see here https://www.python.org/dev/peps/pep-0616/#id26

The PEP authors suggested a kwarg of ``required`` which is certainly better. Maybe ``raise_exception`` would be even more explicit albeit verbose.

It might be a useful feature; consider the following example::

    dogs = ['mydog_spot', 'mydog_sally', 'jill']
    new_dogs = [d.removeprefix('mydog_', required=True) for d in dogs]
    
If there is support for this feature, I would like to work on it. Let me know what you think, and whether you think that ``required`` or ``raise_exception`` is a better name for the keyword argument.

Any kwarg is OK for me, so please do.

@lemburg, hopefully I'm asking the right person... you're down as the devguide expert on unicode and these changes would (I think) need to be applied here::

Objects/unicodeobject.c::12814 unicode_removeprefix_impl

Anyway, do you think this would be a useful feature that you'd like to see added?

Start by presenting this idea on python-ideas list.

I'm +-0 on this. I would write something like this instead:

    assert whatever.startswith(prefix)
    result = whatever.removeprefix(prefix)

Note that if this were to change, the corresponding methods would also have to change on bytes, bytearray, and collections.UserString.