python: overriding access a var

Question

I have a class:

class A:
    s = 'some string'
    b = <SOME OTHER INSTANCE>

now I want this class to have the functionality of a string whenever it can. That is:

a = A()
print a.b

will print b's value. But I want functions that expect a string (for example replace) to work. For example:

'aaaa'.replace('a', a)

to actually do:

'aaa'.replace('a', a.s)

I tried overidding __get__ but this isn't correct.

I see that you can do this by subclassing str, but is there a way without it?

Is there a reason you _don't_ want to inherit from `str`? That would be the right way to do this. — Katriel, Jul 26 '10 at 08:41
well, as the title of the question says, it's a more general question. This solution is good but I think overriding "access a var" will come in handy. — Guy, Jul 26 '10 at 10:05

score 7 · Answer 1 · answered Jul 26 '10 at 08:06

7

If you want your class to have the functionality of a string, just extend the built in string class.

>>> class A(str):
...     b = 'some other value'
...
>>> a = A('x')
>>> a
'x'
>>> a.b
'some other value'
>>> 'aaa'.replace('a',a)
'xxx'

answered Jul 26 '10 at 08:06

David Webb

score 1 · Answer 2 · answered Jul 26 '10 at 08:02

1

Override __str__ or __unicode__ to set the string representation of an object (Python documentation).

answered Jul 26 '10 at 08:02

Mad Scientist

Then use Dave's solution, that should support the whole string functionality. My solution only works for a small subset. – Mad Scientist Jul 26 '10 at 08:12

score 1 · Accepted Answer · edited May 23 '17 at 12:19

1

I used Dave's solution and extended str, and then added a new function:

def __new__(self,a,b):
    s=a
    return str.__new__(A,s)

edited May 23 '17 at 12:19

Community

answered Jul 26 '10 at 09:03

Rivka

3 Answers3