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Welcome back.

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So as we talked about before, a while
loop is generally more capable than a for

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loop but there are few
drawbacks to using while loops.

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The first is that it can be a little bit
more tedious to express the same concept,

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as you might have seen in some
of the code samples from before.

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But the second is that you can get stuck
in what's called an Infinite Loop.

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An Infinite Loop is a loop
that never terminates.

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In other words, your program,
if it could, would keep running forever.

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Now remember that if we have
a while loop like this,

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then every while loop has a condition.

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And by the time we get to
the end of the while loop,

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then we're going to go back to the top and
check if this condition is still true.

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And what that means is that if you
ever run the code in this while loop,

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then it better have a chance of switching
this condition from false to true.

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But if that's not the case, in other
words, if this condition is always true

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and we always reach the end
of this while loop,

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then our code is going to be stuck
in what's called an Infinite Loop.

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Because if we always reach
the end of this while loop,

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then we're always going
to go back to the top.

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And if this condition is always true,

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then we're always going to
run this code once more.

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And that's called an Infinite Loop
because your program would

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keep running infinitely if it could.

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In reality of this textbook
has a mechanism to

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prevent your code from
running too long and

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pretty much every interpreter has some
way of breaking out of an Infinite Loop.

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But they can be frustrating,
nonetheless, and

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they're important to be able to recognize.

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Now this code is actually
stuck in an Infinite Loop.

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So if I ran my code,
now I would see first that my cursor

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is stuck on a pointer, so
that tells me that is something is wrong.

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If I even try to click or type anything

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then I am not going to be able to,
because this computer is working so

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hard trying to run this little
while look that has three lines.

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Now, after a while then,

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the Python interpreter is going to
say that this code ran too long but,

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until then, I'm not going to be
able to do anything on the page.

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So, as it's evaluating this,

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let's try to analyze why we're
actually stuck in an Infinite Loop.

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So, here we go.

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The code finally finished running and

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you can see that it printed out Bugs many,
many times.

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So, I'm going to scroll
to the bottom here.

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You can see that it
printed out Bugs a lot.

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And at the end,

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I'm going to get a message that this
program exceeded the run time limit.

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So in other words,
this program tried to run for too long and

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this probably indicates that your
program is stuck in an Infinite Loop.

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So let's look at why this program
is stuck in an Infinite Loop.

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So here we initialize
the variable b to be 15.

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So that looks good so far and
we say while b is less than 60.

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Okay, so this condition is of course
going to be true while b is 15.

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So when b is 15,
then we're going to run this code.

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And then we say b = 5.

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Hm, well,

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that looks a little bit out of place, but
let's come back to it in a little bit.

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On line 5, we print out Bugs,

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which as you can see gets printed out a
lot because this while loop is run a lot.

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And then on line 6 we say b
equals its previous value plus 7.

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Now, let's come back to
this line b = 5 because

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what assigning b = 5 does here is
it kind of resets the value of b.

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So again our check is
if b is less than 60.

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And so if we keep resetting b to be
5 even if we increment its value

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to be 12 later on by adding 7 to it then
b is still always going to be less than

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60 because every time we run this
loop we reset b's value to 5.

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So maybe if line 4 was accidental,
so if we commented it out,

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then we would actually
be able to run our code.

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So again,

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the problem here is that we were resetting
b to be 5 every time we ran this code.

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So, it's important to be able to
recognize how Infinite Loops occur.

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They can occur in many, many ways.

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So, this example is just one of many ways
to accidentally write an Infinite Loop.

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As you get more experience
in writing while loops,

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you'll become more adept at being able
to identify and fix Infinite Loops.

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That's all for now until next time.