Check maxlen of deque in python 2.6

Question

Hi,
I have had to change from python 2.7 to 2.6.
I've been using a deque with the maxlen property and have been checking what the maxlen is. Apparently you can use maxlen in python 2.6, but in 2.6 deques do not have a maxlen attribute.
What is the cleanest way to check what the maxlen of a deque is in python 2.6?

In 2.7:

from collections import deque
d = deque(maxlen = 10)
print d.maxlen

In 2.6 the deque can be used and the maxlen works properly, but maxlen is not an attribute that can be referred to.

Cheers

Answer 1

maxlen is a new part of deque that was first implemented in Python 2.7. It just doesn't exist in Python 2.6.

That said, there are a few things you can do:

1. Create a new class that inherits all the methods and attributes from deque but also implements a maxlen attribute.
2. Adapt your code so that maxlen isn't necessary

Answer 2

Well, if you don't have the maxlen attribute, you can just steal it from the representation:

>>> import re

>>> d = deque(maxlen=42)

>>> d.__repr__()
'deque([], maxlen=42)'

>>> int(re.sub("\)$","",re.sub(".*=","",d.__repr__())))
42

Yes, I know it's horrible. I would prefer to upgrade to 2.7 myself but sometimes we're not given the power we desire, and we have to resort to kludges like this.

Answer 3

I would create my own deque by inheriting from collections.deque. It is not difficult. Namely, here it is:

import collections

class deque(collections.deque):
    def __init__(self, iterable=(), maxlen=None):
        super(deque, self).__init__(iterable, maxlen)
        self._maxlen = maxlen
    @property
    def maxlen(self):
        return self._maxlen

and this is the new deque at work:

>>> d = deque()
>>> print d
deque([])
>>> print d.maxlen
None
>>> d = deque(maxlen=3)
>>> print d
deque([], maxlen=3)
>>> print d.maxlen
3
>>> d = deque(range(5))
>>> print d
deque([0, 1, 2, 3, 4])
>>> print d.maxlen
None
>>> d = deque(range(5), maxlen=3)
>>> print d
deque([2, 3, 4], maxlen=3)
>>> print d.maxlen
3

Answer 4

I would create my own queue class that inherits from deque. Something like:

class Deque(deque):
    def __init__(self,*args,**kwargs):
        deque.__init__(self, *args, **kwargs)
        self.maxlen = kwargs.get('maxlen',None)

>>>d = Deque(maxlen=10)
>>>d.maxlen
>>>10