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[MUSIC]

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So we talked about variable types, and

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we talked about small transformations.

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So now, let's go to the next step.

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In the next step we're going
to do conditional statements.

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So Esc+M,
I'm gonna define another section here,

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Conditional statements in python, okay.

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So there are various ways to
build a conditional statement

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in Python depending on how long and
how complicated it is.

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So let's do a very simple one.

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For example,
let's say that I want to ask if

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the integer variable i that
I created is equal to 1.

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That's my test.

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And the float variable
that we created is > 4.

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That's my conditional statement.

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It's easy to read, and

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if this is the case, colon,
we put a colon after the if statement.

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We do something.

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Now in Python,
there's no open brackets and

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close brackets like you have in C for
example or in Java.

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All you have to do is put any amount of
spacing or tabulation in the next line.

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And that's what defines kind of the pieces
that will be inside the brackets,

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inside of another programming language.

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And you just keep aligning
them the same way.

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And iPython Notebook is nice
because it does all the tabulation

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automatically for you.

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So let's say if i == 1 and
f > 4 something happen.

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So I'm gonna print

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the value of i is 1 and

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f is greater than 4.

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Now, I'm gonna just print
that if this is the case.

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But I also wanna have another condition,
I wanna have an else condition.

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So in Python,
you could just type else something, but

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I want to have multiple conditions.

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So I wanna do another else if,
if some other condition is true.

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And Python allows you to
concatenate elses and ifs together.

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So if you just create an elif, it's kind
of a cute little syntactic sugar here.

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So if the first condition, i == 1, f > 4
does not hold, ask the following question.

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Is i > 4?

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Or, so there's ands.

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So I'm gonna put a nice little space here.

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Ands and ors, you just say or.

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You don't have any kind of that
fancy vertical brackets or anything.

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Let's just say and and or, f > 4.

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Do something else.

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So our something

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else is print i and

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f are both greater than 4.

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Now if this is not true,
we can add another else at the end.

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So I'm gonna backspace and
align in the beginning.

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Just put another else with a colon at

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the end and say if this is not the case,

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then you say print say both.

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So if this condition is not
the case then what we know.

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We know that i is not greater than 4 and
i is not equal to 1.

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f is not greater than 4.

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So there's some things that have happened.

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So we can just say
something like both i and

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f are less than or equal to 4,
and we also have that,

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well let's say that this is enough.

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Okay, I'm done.

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I'm done with my statement and
now remember the values of i and f.

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I just printed it out here.

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i was 4 and f was 4.1.

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So if you go through the first line,
you notice that i is not equal to 1.

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So you go to the next line,
you notice that i is not greater than 4.

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So you go to the next line, you're just
going to print this last statement,

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both i and f are less than or equal to 4.

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So if I do Shift+Enter, I execute
this conditional, and there you go.

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i and f are both greater than 4.

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So, that was good.

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We built our first conditional here.

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It's all fine.

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Now that we've done some conditionals,
let's do some loops.

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So, again, I'm gonna go into

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the editing mode markdown Esc+M,

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and we're gonna do some conditional loops.

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So, what kind of conditional
loops can we do in Python?

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We can do for loops.

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So for example, we can do a for,
so remember we had a list.

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This is kind of fun.

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So let me just print it
to remind ourselves.

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So if I print a list l, that we built
in the beginning, it was 3, 1, 2.

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So let's do for
a loop that iterates over that list.

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So for, let's say element in l For

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each element in l,
I'm going to do something.

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I'm going to print the element.

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So, this goes element by element of l.

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And I just call it element,
I could have called it anything.

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Let's call it e.

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So, for e in l, print it.

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So it's going to go 3 print,
1 print, 2 print.

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Let's execute that and you see 3 1 2.

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And notice in Python when you call print,
you always insert a new line at the end,

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so you've got 3 1 2 in your lines.

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Now that is a simple for loop.

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Lastly, let's create a simple while loop.

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So you can do fors, you can do whiles.

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So for example, while might say,
while a counter is,

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let's just say < 10, do something.

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So I'm going to print the counter.

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And, I'm going to add 1 to the counter.

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So, I'm going to say counter, += 1.

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So, what this is going to do is create
a counter and print it, and add 1,

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print it, add 1, until we get to 10,
when it's going to stop.

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So, notice that we never initialize
counter, which should give us an error.

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And so let's just run it and
see what happens.

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We got an error, and
whenever you get an error in Python,

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the error messages sometimes
can be a little scary.

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So you just go here and
look at the name of error.

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And it says down here,
name counter is not defined.

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Remember, we never initialized counter.

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And it actually goes and

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tells you a little above what line
of the code that error occurred in.

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So when it first started test
while the counter is less than 10,

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counter is never initialize, it broke.

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So let's go back and edit.

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I'm gonna insert a new line here.

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Let's initialize a counter first
through any number less than 10.

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So, how about 6?

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So, counter = 6, and
I'm just gonna execute again.

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And you'll see now it prints 6, 7, 8, 9.

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When it gets to 10, stops.

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[MUSIC]