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Most sequences have a few useful methods that you can do on any sequence.

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The way to call that method is to save the sequence name and then the method name.

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So, I'm going to go over two methods on sequences, count and index.

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So, suppose that we have a,

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a string and we want to find out how many times

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a given character or a given sequence of characters appears in the string a?

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The way that we would do that is using the count method.

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The way to call count is we say the name of the sequence whether it's a string,

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integer, or tuple that we want to count on.

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So here, we want to do a count on a.

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So, I say a, and then the dot or period,

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and then the method name that we want to call,

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dot count, open parentheses.

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In the case of count,

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we pass in a string which is the sequence of characters that we actually want to count.

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So, on line two,

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we're counting the number of characters e in a,

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and then we close parenthesis in order to finish that method call.

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One thing to note here is that count is case sensitive.

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Meaning that we don't count capital e's if there are any capital e's in a.

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We would only count lowercase e's.

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So here, when we say printout a.count("e"),

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then we look for the number of e's that are in the string a.

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So, in this case, we should get one,

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two, three, four, five.

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In addition to counting individual characters,

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we can also count substrings.

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So here, we're counting the number of times the substring ha appears.

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So, we should get one, two.

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So, let's run our code just to double check.

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So, we can see that we get five e's and two times that ha appears in this string a.

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Just like strings, count also works on lists.

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So here, we have a list z that has 1,2,3,4,5,6,7,8,9,10 items.

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So, on line two,

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if I comment out the rest of these lines,

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on line two, we're finding out

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how many times does the string four appear as an item in z.

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One thing to note here is that the string

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four is an entirely different thing than the integer four,

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which we have here, here, and here.

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So, when we say print out z.count the string four,

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then we're going to actually get zero because no item in z is the string four.

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If we instead counted for the integer four,

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then we would get what we might expect.

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So, we'd get one, two,

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three because there are three integers four in our list z.

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So, if I hit save and run again,

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then I'll see that I get three when I print out z.count the integer four.

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Here's something that's a bit trickier.

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So, let's suppose that I say z.count the string a.

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Now, we can see that in our list z,

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the letter a appears a few times.

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So, in the first item of z,

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a appears in atoms,

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and then it also appears in the last item.

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So, we might almost expect the result to be two.

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But if we actually run our code,

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then we'll see the result is zero.

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Now, why is that?

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Well, when we call z.count the character a,

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what we're looking for our items in z where the item itself is the string a.

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So, the fact that a just happens to be

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a character in this larger string doesn't matter to Python.

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What Python would care about is,

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is the value actually the string a?

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So, if I had one item here that was the string a,

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then I would get count one.

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But because this instead is the string atoms,

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then I get zero when I look for the number of a's.

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On line five, we do z.count("electron"),

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and when I look, I see that there is one,

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two electrons in z.

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So, I should expect line five to print out two.

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Now, let's go on to another useful method named index.

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Index finds where an item is.

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In the case of index,

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it searches for the first time that a given string or item appears.

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So, let's suppose that on line one,

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we're creating this string,

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"Pull out your music and dancing can begin".

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Now on line two, we create this list that has 1,2,3,4,5,6,7,8,9,10 items.

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Now, when we print out the value of music.index of m,

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then we're printing out the first or leftmost index where lowercase m appears.

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So, if I comment out the rest of these lines,

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and only print out the value of music.index of m,

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then we should get the index of the first m. Just to find out where that is,

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we should get it at

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0,1,2,3,4,5,6,7,8,9,10,11,12,13,14.

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So, this m, which is the first term leftmost m that appears is at index 14.

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What that means is that the value of this overall expression,

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music.index of m is going to be 14.

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Let's run our code and make sure that that's the case.

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So, we see that we get 14.

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On line five, we print out the value of music.index of your.

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So, what this is going to do is it's going to search for

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the first time that this substring 'your' appears,

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and it's going to print out the index where it starts.

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So, we should expect that to be zero, one, two, three,

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four, five, six, seven, eight, nine.

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So, when we run this and we get nine as a result because 'your' starts at index nine.

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Now, index works with lists as well as it does with strings.

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So, if we print out bio.index of metatarsal,

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then we get the first index where metatarsal appears.

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So here, on bio,

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that should be index zero.

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Even though this appears multiple times at index zero and one,

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index always gives us the first or leftmost index where it appears.

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So, nine, seven should print out zero.

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On line eight, we print out bio.index of an empty list.

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This is going to search for the first empty list in this list bio.

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So, the index should be zero,

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one, two, and we find it at three.

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So, when we run this,

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we should expect three.

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Then finally on line nine,

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we print out bio.index of 43.

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So, that's going to be zero, one, two,

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three, four, five, six.

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Now, one thing to note for index is that if something is actually not in the sequence,

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then we get a runtime error.

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So, if we create this list,

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seasons and set its values to be winter,

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spring, summer, and fall.

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Then we search for autumn,

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note that autumn is not in here because we instead wrote fall.

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So, if we print out seasons.index of autumn,

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then we're going to get a runtime error,

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and that runtime error is going to print out that the item that we searched for,

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in this case, autumn was not in our list, seasons.

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Okay. So, let's answer some questions about count and index.

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So, this question ask,

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what will be stored in the variable ty below?

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So, we say ty is qu,

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which is this string dot index of we.

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So, this is searching for the first time that we find the string we.

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So, that's going to give us zero, one,

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two, three, four, five.

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Again, when we search for a substring,

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we search for where it starts.

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So, that's going to give us five.

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Next, what will be stored in the variable ty now?

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So, we say ty is the string qu.count of we.

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So, here we're searching for how many times does

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this substring we appear in this string qu?

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So, we see we right here at the start of welcome,

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here at the start of week.

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We might think that we actually see it here,

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but if you look closely,

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this is actually a capital w and not a lowercase w. Now,

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remember that Python is case sensitive.

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So, capital w is a completely different thing than a lowercase w. So,

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Python isn't actually going to count this.

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So, Python isn't actually going to count this we because it contains a capital w. So,

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the end result here is that we get two.

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So here, we're asked, what will be stored in the variable ht below.

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So, we have room set to a list with one, two, three, four,

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five, six Items, and we asked for rooms.index of garden.

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So, we're going to search for is garden in this list rooms.

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So, we see it's not here,

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nor here, nor here,

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nor here, nor here, nor here.

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Garden isn't anywhere in this list.

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Remember that when we tried to do index on something that's actually not in the list,

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then we get an error.

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So, the answer here should be an error.

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That's all for now, until next time.