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- [Instructor] Hi and welcome back.

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We are here on the dictionaries

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and students coding exercise,

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and this is a slightly longer
and more complex exercise,

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because we are progressing
through the course,

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and we are getting deeper into Python.

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So let's have a look.

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It has three parts.

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First one, create a dictionary
variable called student.

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It's partially defined here,

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and we're gonna look into exactly

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how we create this variable.

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Then we're going to modify
a variable called grades

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down here so that it contains

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the value of a dictionary's key.

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We've got more information
on the comments.

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And finally, we're going
to implement a function

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calculating a total average
grade for a class of students,

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with again, good more
information on the comments.

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Let's go straight in.

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For the first one, we're
going to create a variable

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called students that
had a dictionary in it,

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and the dictionary has
to contain three keys,

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name, school, and grades.

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Okay, so let's do that first.

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The dictionary as we know

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is with opening and closing curly braces.

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And then we're gonna
have name is something,

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school is something,
and grades is something.

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We don't know what yet.

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Let's have a look.

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The values for each must be Jose for name,

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computing for school, and a topple

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with the values 66, 77, and 88 for grades.

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Let's do that.

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The name has to be Jose, which is my name.

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School has to be computing.

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Definitely not that,
computing, there we go.

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Normally I can spell.

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And that the grades have to have a topple

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with the values 66, 77, and 88,

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so we're gonna delete that
string, quotation marks,

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and we're gonna put the topple
in here, 66, 77, and 88.

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Notice that because this is a topple

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with multiple values, we
don't need a comma at the end.

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In fact, we should not put it in there.

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Okay, so now we have our student.

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And we can move on to the
next set of instructions.

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Assume the argument, data,
which is the argument

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to this function here, is a dictionary.

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Modify the grades variable so it accesses

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the grades key of the data dictionary.

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Okay, so the grades variable right now

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doesn't equal anything,

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and we have to make it
equal to the grades key

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of the data dictionary.

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Well, we know how to access
a key in a dictionary.

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We just have to do data,
which is our argument,

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our dictionary, grades.

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There we go.

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Now, the grades variable is accessing

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the grades key of the data dictionary.

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There we go.

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Some other students have
done this, student['grades'],

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and that is a totally
reasonable thing to do,

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except the student variable
is a global variable

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that is available for every
method, every function.

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So whenever we call this function here,

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this average grade
function, we're always going

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to use this variable here

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instead of the argument, which is data.

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This means that if we call average grade

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with this variable here as an argument,

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then it will work fine.

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But if we call it with
a different argument,

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then it will still use the
student dictionary here,

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and it will return incorrect data.

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So make sure to use, as, oh sorry.

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I'm pressed them to pressing
save on every few seconds,

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make sure to use that data argument there.

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And finally, implement the function below,

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which is average grade for all students.

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Given a list of students,

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which as we know are dictionaries,

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calculate the average grade of the class.

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So, given a list of students,

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that's this student list here,

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this is the list of our students,

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we must add all the grades
of all students together,

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and you must also count
how many grades there are

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in total in the entire list.

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Okay, so we have two
variables, total and count.

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Presumably, total must be
the sum of all the grades,

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and count must be the amount
of grades that we have.

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And from each student
in this student list,

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we have to add to these two variables

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so that at the end, it returns

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the total divided by the count,

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which should give us the average.

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So, how do we calculate the total?

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Well, we can say total
equals total plus the sum

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of the student grades.

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And then the sum is going
to add up all the values

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in a list or a topple,

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and the student is, each of the students

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in the student list, student grades

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will give us that topple.

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Sum will give us the total of that topple,

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and it's going to modify
the total variable

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so that it is the existing number

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of total plus the sum
of this other student,

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and the count is going
to be count equals count

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plus the length of the student grades.

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And that is going to give us

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the count of student
grades for this student.

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It's gonna add it to the existing count,

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and it's gonna override the count variable

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with that value.

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And then at the end,
we're gonna return total

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divided by count, which is
going to give us the average.

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Because it's quite common
to do total = total +

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and count = count +, with any variable,

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Python gives us a shortcut,

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which is +=, +=.

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So this means the same thing.

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Total is gonna add to the total

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the sum of the student grades,

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and it's gonna add to the count

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the length of the student grades.

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Notice that if you do just count plus

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the length of student
grades, you're calculating

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what you want, but you
are not assigning it

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back to the variable, so
hence, this would not work.

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You need the equal sign there.

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Let's check the solution,
and it should give us

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that all is correct.

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And indeed, there we go.

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So now we've learned a bit more

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about how this sort of works.

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Hopefully you managed to do
this on your own earlier,

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but if not, hopefully
this clears things up.

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I'll see you on the next video.