[Tutor] Tuple indexing

[Ian D]

Thanks.


My original approach was to use a list as it seemed to lend itself to that. But as I referred back to the code I was adapting from I ended up using that example with a Tuple. I may look at changing it again, but for now I need the thing to work asap.

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> To: tutor at python.org
> From: __peter__ at web.de
> Date: Wed, 11 Mar 2015 16:35:09 +0100
> Subject: Re: [Tutor] Tuple indexing
>
> Ian D wrote:
>
>> Hi
>>
>>
>>
>> I have seen some examples that seem to use a tuple with a method called
>> index()
>>
>>
>> The original code I was looking at had this sort of thing:
>>
>>
>>
>
> Hi Ian! Please don't use that much whitespace. It makes your post hard and
> unpleasant to read. Thank you.
>
>
>> SENSORS = ('sensor1', 'sensor2')
>>
>>
>>
>> pin_index = SENSORS.index("sensor1")
>>
>>
>> so the result is that pin_index the is equal to 0
>>
>>
>> I then read that a Tuple has no attribute index on this site
>> http://www.diveintopython.net/native_data_types/tuples.html
>
> Dive into Python is quite old.
>
>>>>> t.index("example")
>> Traceback (innermost last): File "<interactive input>", line 1, in ?
>> AttributeError: 'tuple' object has no attribute 'index'
>>
>>
>>
>> The example seems to work with 2.7 and 3.3 for me.
>
> The tuple.index() method has been added in Python 2.6:
>
> https://docs.python.org/2.6/whatsnew/2.6.html
>
> """
> Tuples now have index() and count() methods matching the list type’s index()
> and count() methods:
>
>>>> t = (0,1,2,3,4,0,1,2)
>>>> t.index(3)
> 3
>>>> t.count(0)
> 2
> (Contributed by Raymond Hettinger)
> """
>
>> But I don't find much documentation on indexing Tuples using this method.
>> I am just wondering if there is more specific documentation on using
>> Tuples this way
>
> Many Python coders don't use tuples to look up an item index; the
> traditional application is to pass multiple values around, e. g.
>
> def extent(thing):
> x = calculate_width(thing)
> y = calculate_height(thing)
> return x, y
>
> width, height = extent(picture)
>
> portrait = width < height
>
> In the example you have to know the index beforehand, by reading the code or
> its documentation rather than going through all items for a matching item.
>
> When you want to treat all items in a tuple uniformly in most cases using a
> tuple is a premature optimisation; use a list or set unless you can name a
> compelling reason not to.
>
> Your sensors example could be solved with a dict:
>
> sensors = {"sensor1": 0, "sensor2": 1}
>
> pin_index = sensors["sensor1"]
>
> This approach will still work well for huge numbers of sensors (constant
> time or O(1)), unlike tuple/list.index() where the average lookup time grows
> with the number of items in the tuple or list (O(n)).
>
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