Is there a library function that performs binary search on a list/tuple and return the position of the item if found and &#39;False&#39; (-1, None, etc.) if not?

I found the functions bisect_left/right in the [bisect module](http://docs.python.org/library/bisect.html), but they still return a position even if the item is not in the list. That&#39;s perfectly fine for their intended usage, but I just want to know if an item is in the list or not (don&#39;t want to insert anything).

I thought of using `bisect_left` and then checking if the item at that position is equal to what I&#39;m searching, but that seems cumbersome (and I also need to do bounds checking if the number can be larger than the largest number in my list). If there is a nicer method I&#39;d like to know about it.

**Edit** To clarify what I need this for: I&#39;m aware that a dictionary would be very well suited for this, but I&#39;m trying to keep the memory consumption as low as possible. My intended usage would be a sort of double-way look-up table. I have in the table a list of values and I need to be able to access the values based on their index. And also I want to be able to find the index of a particular value or None if the value is not in the list.

Using a dictionary for this would be the fastest way, but would (approximately) double the memory requirements.

I was asking this question thinking that I may have overlooked something in the Python libraries. It seems I&#39;ll have to write my own code, as Moe suggested.

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Binary search (bisection) in Python