custom string class

Here is how to make a subclass of string which has all the same operations available, but which returns instances of that subclass:

import inspect

import functools

class MyStr(str):

    def __radd__(self, other): 

        return MyStr(str.__add__(other, self))

    def __repr__(self): 

        return self.__class__.__name__ + str.__repr__(self)

def _mystr_wrap(f):

    @functools.wraps(f, ('__name__','__doc__'))

    def g(*a, **kw):

        res = f(*a, **kw)

        if res.__class__ == str:

            return MyStr(res)

        return res

    return g

for name, f in inspect.getmembers(str, callable):

    #skip some special cases

    if name not in ['__class__', '__new__', '__str__', '__init__', '__repr__']:

        setattr(MyStr, name, _mystr_wrap(f))

>>> MyStr("cat")

MyStr'cat'

>>> MyStr("cat")+"dog"

MyStr'catdog'

>>> MyStr("cat")[1:]

MyStr'at'


Note: if you find yourself actually doing this, it is probably a bad code smell :-)

making your class work with built-in math functions

Just add __float__ and/or __int__.  Then the built-in math functions, or anything that sanitizes its input via int() or float() will see your objects as a numeric type.


>>> import math

>>> class B(object):
...    def __float__(self): return 0.5
...
>>> math.sin(B())
0.47942553860420301