collections.deque get index of element by value

Question

For list we can get index of element list_name.index(3)

How to get index of item in deque.

ex: d_list = deque([1, 2, 3, 4]) what is the best way to get the index of element 3.

Edit: I am using Python 2.7.6

Answer 1

Just use it like regular lists:

>>> d_list = collections.deque([1, 2, 3, 4])
>>> d_list.index(3)
2

Edit: This is only possible in Python 3.5 right now

Answer 2

According to the pythons docs, if you have python3.5 or better, you can use index (as per tobspr's answer).

For older pythons, you can convert the deque to a list and then use index:

In [5]: from collections import deque

In [6]: d_list = deque([1, 2, 3, 4])

In [7]: list(d_list).index(3)
Out[7]: 2

Answer 3

If you are using Python 2.x, deque is not a good choice if you want to do lookup. You can either use list or do the following using enumerate():

>>> def index(element, queue):
...     for i, ele in enumerate(queue):
...         if ele == element:
...             return i
...     raise ValueError("{} is not in queue".format(element))

>>> index(2, deque([1, 2, 3, 4]))
1

Alternatively, you can implement your own queue:

>>> class IndexedDeque(deque):
...     def index(self, element):
...         for i, ele in enumerate(self):
...             if ele == element:
...                 return i
...         raise ValueError("{} is not in queue".format(element))    

>>> d_list = IndexedDeque([1, 2, 3, 4])
>>> d_list.index(2)
1