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So I want to introduce one more operation on strings, which

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we'll find very useful, which is the Find operation. It gives

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us the way in a big string to find some sub-string

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that we're looking for. The way we use Find is a little

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different from the way we've used other operators so far. Because

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Find is actually a method, and what that means is it's

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a built in procedure provided by Python. We'll be able to

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define our own procedures soon, we'll get to that in unit two.

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Find is a procedure that operates on strings, so we use it by having

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a string followed by .find, followed by

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a parentheses, then we pass in another string.

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Which is the string that we want to find in

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the first string. And the output of Find is the

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position in the string where that sub-string is found, the

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first occurrence of the string. So, if that string happens

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to occur in more places than one in the

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input string, the result of find is always going to give

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us the position. That's the number where the first occurrence

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of the sub-string occurs. So the output of using Find

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will be the first position in the search string, which

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is this blue string right here, where the target string,

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which is the purple string, occurs. So that will be

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a number. If the target string is not a found anywhere

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in the search string, then the output would be negative

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1. So let's try a few examples to understand how

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that works and we'll do this in the Python interpreter.

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Here I've initialized the variable Pythagoras to hold the string here

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that's been attributed to Pythagoras. We don't know if

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he really said it. But it says there's a geometry

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in the humming of strings, there is music in

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the spacing of spheres. So now, we have that variable

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initialized, so I'm going to invoke Find, using Pythagoras as

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the string that we're searching in, and that's the value

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that we initialized it to with a string, passing in

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as the search string the string string. When we run

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this, we see that we get 40 as the result. If we counted, this is position 0, we

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would see string starting at position 40. Since I

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don't want to count that far, we can use our indexing

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to see if that's right. So let's print Pythagoras

40
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starting from index 40, we could print all the

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way to the end using a colon. And, when

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we run that, we see that it starts with string

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which is what we found with the Find. We can search

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for other positions if we search for Pythagoras the single letter T.

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Well that matches the beginning, so we should find the resulted position

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0 which is what we get and we can look for sphere.

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[BLANK_AUDIO]

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That will match sphere at the end. We get

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position 86. Let's print the quote from position 86. And

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we see the end of the quote starting from sphere. [SOUND]

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If we search for a string that's not in the string

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that we're using as the search string, so let's look for

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say, algebra, which was not in the quote from Pythagoras, we

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get the output negative one. That means the string was not found.