safe.py

SAFE = True
MASK = "*"


def mask(val):
    return MASK * len(val)


def value(val):
    return mask(val) if SAFE else val


DANGEROUS = [
    "__str__",
    "__repr__",
    "__add__",
    "__mul__",
    "format",
    'capitalize',
    'casefold',
    'center',
    'format_map',
    'ljust',
    'lower',
    'lstrip',
    'splitlines',
    'strip',
    'rstrip',
    'swapcase',
    'title',
    'upper',
    'join',
    'zfill',
    'replace',
]


class Wrapped:
    def __init__(self, orig):
        self.orig = orig

    def __get__(self, instance, owner=None):
        def _wrapped(*args, **kwargs):
            return value(self.orig(instance, *args, **kwargs))
        return _wrapped


def wrap_dangerous(cls):
    for name in DANGEROUS:
        orig = getattr(cls, name)
        setattr(cls, name, Wrapped(orig))
    return cls


@wrap_dangerous
class SafeString(str):
    pass


sstr = SafeString

if __name__ == "__main__":
    print(str(sstr("foo")))
    print("{} bar baz".format(sstr("foo")))
    print(sstr("foo {}").format("bar baz"))
    print(sstr("foo") + " bar baz")
    print(sstr("foo").lower())