WEBVTT

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let's go back to our initial fruit
Python file which I called shelve for example but it was

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dealing with fruit as you can see here I want to
show you what happens when we assign a new

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key a new value I should say to a key for
example we've got this code here come

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down here after or before the close after
we printed out these items here we could

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do something like fruit...
and just to

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confirm it's been updated we can put...
 and we can do print....

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in double quotes should say....
 and grab the value using the key, and we are gonna leave fruit.close() in as

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well and leave the final printing so lets do
that and see what happens to lime bearing

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in mind on line 9 we defined it as a 
sour green citrus fruit then on 14 we

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changed the definition and will run that and again
need to make sure to select the right program

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because initially when I first created the
class of you recall I called it shelve and

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this is the configuration and not the
actual class name which can be confusing so

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we go in there if we want to change that probably a
good idea to do that changed the name

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we should be able to change that now, will name it fruit
 which makes sense to us and click on apply

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and save and now we have fruit their which
makes a lot more sense so know if we run

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that way or selecting up here you can see
we've got lime is now great with

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tequila as you can see there so
obviously it was updated and we saw in

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the previous video that the when we misspelled the word

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engine and removed an e at the end when we
attempted to access the key that

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doesn't exist we got an error and we can
use the get method to avoid that so we

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could do something like, will comment some of this code now, so comment the code here and leave the close

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line and remove the print as well

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we don't need it anymore, the code above that we will put a while...

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...will ask for some input....and will put if....thats the case we

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are gonna break

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otherwise we gonna do a look up so...

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and use the key that is
entered by the user

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who type that in and trumpeted it out, description... and also leave line 27 and then we

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broken out of the loop we close the
shelve down because we finished

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processing so we try running that now
so type a valid one, lime a sour green

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citrus fruit we could write grape that work
lets try typing that is not

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in there Strawberry we get none and I can quit out of that as well, we

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can also specify the default value to return
if the key is not present and dare I say it

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again just like a dictionary and if you
remember how to do that we come down here and we

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put in the fruit.get..if we run that...enter a valid one like lemon to check if its working

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try something like melon

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and I don't have a melon instead of saying none which
obviously is a lot more user-friendly, and ill quit out of that

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the same effect can be obtained by
checking if the key itself is in the

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shelve before attempting to retrieve and print
the value using in and again it's just like a

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dictionary so we could modify a program
they so lets just changed that shelf_key lets just

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refactor that so right click refactor  and rename
that we raname that to dict_key and refactor it

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a few other changes there instead of us having
to rename it 4 5 places, please enter a

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fruit

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if the dictionary key equals quit we still
break as we do before, what we can do is

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if....only then we do description is fruit.get, will change that description = fruit

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dictionary key because we don't need to do that anymore and put...and obviously we don't need that

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anymore because we determined that this dictionary key does
exist in our shelve and we put the print

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description on that line as well, also put the else
 and that's where we print the item, so we....we leave the fruit.close() alone, so we run that again

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enter lemon , apple, put melon

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we don't have a melon, so it still work in the same as it was before
we've just done the test this time

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beforehand

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instead of only printing it out putting
it out afterward we retrieve it

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so just a different way of doing it now the lecture on dictionaries

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we pointed out that the keys themselves are
unsorted and the actual order is

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undefined for dictionary now the same is true for a shelve
the good thing though is that if

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iterate through the keys of our fruit and print
them they may  be in alphabetical order

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and that's not surprising as the shelf is
implemented using a data base and just

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as an example of that ill comment out the code
the while loop because  we don't need it any more we could do

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something like....

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print...

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so we are printing them out like so
if we run it, in this case its not showing

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in alphabetical order but it does on some systems so keep that
in mind again because it's coming from

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a database but you can't rely on that or
assuming it does in this case you can see

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base on the keys in the values they aren't
sorted in alphabetical order so what you

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really want to do is ensure that you get a
sorted list first so in other words if

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you need to ensure that you want to sorted
list to be outputted you need to sort

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those keys first so how would you go
about doing well we got our fruit open

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I'm going to comment this, because obviously
we written to it and each time we are running it we save it again which we don't

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need to do so comment those out and
I'm gonna put here ordered keys...

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...and you've seen this before..

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this its going to be...because we wanted to use
these sorted keys and we go through and print them out

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noticed that with ordered keys we
still using the look up key to

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grab the value-added because the keys are now sorted we should

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get the output showing in alphabetical
order so run that now you can see now,

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I've done that way we are getting the output in
alphabetical order which is great even

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if the shelf appears to return
the keys in order on your implementation

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of python which i believe it doesn't Linux
but not necessarily you can't rely on it

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your clearly saw when I was running in
 a MAC without the sort code in it didn't

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sorted alphabetically for us
automatically so you really want to do

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something like this

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you want guarantee it can be sorted in that order
now the values method

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values items methods of shelve behave as do for a dictionary as well interesting

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enough though the actual objects
returned

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are not the same type and which type 
would depend upon the implementation now

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what I'm gonna do is show another example of that we're gonna type some code just gonna print the values

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on shelve and then the items
which is just a sequence of

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tuples to show yo what I mean, I'm gonna comment that code out, gonna go here and start and we're gonna do....

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...and the last line we obviously

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leave the fruit.close()

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so if we run that, a typo there fruit.values it should be
run that again and there you go

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instead of dict_values and dict_items are objects these

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methods that were using when called on
the shelve returned values of view as you

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can see, values hear about this line output there and also return an item view as well

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names of these objects really makes it
clear that they view objects which what they are

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can't modify them and that changes to
the underlined lines shelve which will be reflected in them

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like the dict_keys the dict_values
and of course the dict_items

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objects that we've already
seen in previous lectures now in terms of

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behavior though code that works when
using a dictionary and its view objects

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will almost always continue to work if
you replace the diction with a shelve so

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even if you get a different objects back
essentially the code is still going to work on

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most cases without any modification the
initialization will be different and the

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shelve has to be close but most of the
work up to that point will work having

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said that is one really important
difference between dictionaries and

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shelves a shelve key must be a string and
dictionaries themselves can accept any

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immutable object as a key as we talked
about

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but again a shelve will only accept a string
ok so that is it for now on the next video

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we're going to continue our discussion
and look at updating items stored in a

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shelve so see you in the next video