Let's define a string first string is a sequence of characters, meaning letters, numbers and other characters like the dollar signs, spaces and punctuation marks, enclosed by single quotes, double quotes or even triple quotes when spending multiple lines. So let's define a string and assign it to a variable. I'm going to create a variable named my string and assign it the following value. Now checking the results, my string, so we use double quotes for defining the string Next, using single quotes and checking the results again, so the result is the same right? Okay. Now what do we need triple quotes for when we need them whenever we want to enter a string on multiple lines, for instance, a comment in our code.

Let's see how can we do this? Let's assign the same text to the string variable, this time with each word Being on a separate line. So remember that after each word you have to hit enter to write the next word on a separate line. Finally, you should end the string with the same set of triple quotes, and hit enter for the last time. Now let's check our variable my string. It looks like we have something new here.

What with all the backslash ends between the words of the string? Well, backslash n is called a new line character. And it signals a new line being created at that particular point in the string. In plain language, it means that we are inserting a break and a new row, a new line in our text. Okay, so how we can get rid of them. It really looks weird this way, right?

Don't worry, it's simple. We just have to add the backslash. Wherever we want a new line to be inserted. This translates to something like go to the next row and continue the text there. So let's try this again. So we have a backslash here.

Another one here, and the same for the following words, except for the last word in the string. Now let's hit ENTER again and check our variable. Okay, it works no more newline characters. The insertion of backslashes is called escaping the newline characters. Remember this term, because we will use it again later in the course. Now, let's talk about indexing.

And this concept applies to other data types as well. Python uses indexes to mark the position of an element within a sequence of elements. A string is a sequence of elements, and the elements of a string all of the characters themselves one character, one element, the first element of any sequence when counting from left to right, has the index zero. And then the second element of the sequence has the index one. The third element is positioned at index two and so on. So when using indexes, remember to always start counting from zero.

When counting backwards from right to left, the first index will be minus one. So the last character in a string will have index minus one. When looking from right to left, indexes are enclosed by square brackets when we want to access some literal string. Let's see this in practice. Let's create another variable called string one and assign it the value Cisco router. So string one equals in between double quotes Cisco router now how to extract the first character of this string by using an index of course, and As stated before, that would be index zero.

So to access the element of string one positioned at index zero in the string, we should type the following the name of the variable string one and then without inserting any spaces, the index number in between brackets. So okay, now let's hit enter. This returns to it See, which is correct because this is the first character in the string. Now let's find the third character of string one. What index should we use? index two, right?

So string one of two returns s, which is indeed, third character in our string. Now let's see the sixth element, we would need string one of five, right? So let's check this. Okay, that would be the space character in between the words Cisco. And router. Yes, spaces count as characters.

Now for the negative indexes, let's access the last character in the string, we will use index minus one, right? So string one of minus one returns the letter R. Good. What about string one of minus four? Who would that be? Well, let's count minus one is r minus two is E minus three is T and minus four would be the letter you sold Let's check this. And indeed, we are correct.

One more thing on indexes. What if we enter an invalid index for our string? Let's see, what do I mean by that? First, let's find out the length of string one, we can count how many characters are in that string visually. But what if we have a very, very, very long string, maybe a newspaper page. Python has a solution for this, and it is called the Len function.

This function is easy to use just type Len, and without any spaces after it, and the variable name pointing to our string in between parentheses. So Len of string one returns the number of characters, which is 12. Now back to the first question, what happens if we enter an invalid index? Well, let's try it. String one has 12 characters. So starting at index zero and counting from left to right, the last character in the string should have the index 11 right?

So string one of 11 returns are which is correct. Now let's see what happens if we enter a string one of 20. Let's say, well, we got an error, let's celebrate it is one of the first errors we see in this course, errors are a great tool for learning and troubleshooting your code, so don't feel them at all. Now, let's read the error text. It says index error. That is the type of the error.

There are many types of errors in Python, and we will go through the most common ones later on in the course. Next, it says string index out of range. So Python found out that we've typed in an invalid index in between the square brackets and told us that the index is indeed out of range, because the 12 characters string can't have a character positioned at index 20 obviously, now it's time to have a look at some string operations and methods that will help us work with this data type.