Tor Erik Soenvisen wrote:
> What do I need to do to make the code below work as expected:
>
> class str2(str):
>
> def __setitem__(self, i, y):
> assert type(y) is str
> assert type(i) is int
> assert i < len(self)
>
> self = self[:i] + y + self[1+i:]
'self' is a local variable; assigning to it rebinds it but has no effect
outside of the __setitem__() method.
> a = str2('123')
> a[1] = '1'
> print a
> 123
> The print statement should return 113
You have to start from scratch as a strings are "immutable" (once created,
their value cannot be changed).
>>> class mutable_str(object):
... def __init__(self, value):
... self._value = value
... def __setitem__(self, index, value):
... self._value = self._value[:index] + value +
self._value[index+1:]
... def __str__(self):
... return self._value
...
>>> a = mutable_str("123")
>>> a[1] = "x"
>>> print a
1x3
Peter
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