Seems like I want a pre-processor, but...

[Fredrik Lundh]

Russell Warren wrote:

> For example, I've got a bit of python 2.3 code that uses
> collections.deque.pop(0) in order to pop the leftmost item.  In python
> 2.4 this is no longer valid - there is no argument on pop (rightmost
> only now) and you call .popleft() instead.

the collections module was added in 2.4, so it's not clear what code you're
really using under 2.3.  but since it's not a standard module, maybe you could
add the missing method yourself ?

> I would like my code to work in both versions for now and simply want
> to add code like:
>
> if sys.version[:3] == "2.3":
>   return self.myDeque.pop(0)
> else:
>   return self.myDeque.popleft()
>
> but am recoiling a bit at the unnecessary conditional in there that I
> think will be run on every execution - unless the compiler has some
> magic detection of things like sys.version to compile out the
> conditional as if it were a preprocessor directive (seems highly
> unlikely!)?.
>
> What is the pythonic thing to do?

fork the function/method:

    if sys.version_info < (2, 4):
        def myfunc(self):
            # using deque emulation
            return self.myDeque.pop(0)
    else:
        def myfunc(self):
            return self.myDeque.popleft()

or wrap the non-standard deque class in a compatibility wrapper:

    if sys.version_info < (2, 4):
        class mydequeclass(deque):
            def popleft(self):
                return self.pop(0)

    ...

    return self.myDeque.popleft()

</F>