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

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

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

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

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

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

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

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

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

a string followed by .find, followed by

a parentheses, then we pass in another string.

Which is the string that we want to find in

the first string. And the output of Find is the

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

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

to occur in more places than one in the

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

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

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

will be the first position in the search string, which

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

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

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

in the search string, then the output would be negative

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

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

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

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

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

in the humming of strings, there is music in

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

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

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

that we initialized it to with a string, passing in

as the search string the string string. When we run

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

would see string starting at position 40. Since I

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

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

starting from index 40, we could print all the

way to the end using a colon. And, when

we run that, we see that it starts with string

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

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

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

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

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That will match sphere at the end. We get

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

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

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

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

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

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