The force statement is used whenever you want to iterate over a sequence and execute a piece of code for all or some elements of that sequence, list or string or whatever sequence you have. Let's start with an example of iterating or looping over a sequence. And first, let's define a list inside the new Python file. Let's name this file four.pi. Four and now let's change the extension dot p y instead of txt. Yes, let's open the file with notepad plus plus.

And now let's define a list. This one right here having these elements Cisco HP, Nortel, Avaya, and Juniper. Now let's see how we can work with the for loop. First, you will notice that there are some similarities to the if Elif else syntax, meaning that the colon is again used to signal On indented code follows the for statement. And speaking about indentation, we must indent the code inside the for loop using the tab key. In order to separate it from the code that follows.

We start by typing in the for keyword. Then we enter the iterating variable, which is an user defined temporary variable. So you can name it however you like. Let's say each vendor, then we type in the in keyword. To tell Python that we are going to iterate over the sequence following this keyword. And finally, we enter the sequence itself, followed by a colon.

So let's enter the name of our list vendors, colon, then let's say print each vendor. Let's save the file. And now let's run it using the windows command line. So CMD, Python, D four dot p y and this is the result we get each of the vendors inside The list printed out on the screen. So I named my list in such a way that it reflects my specific needs vendors. Then I told Python that it should assign each element in this list to the iterating variable called each vendor, then execute the indented code below for every element until all the elements in the list are exhausted.

So Python did this and printed each item in the list. Of course, you can have multiple lines of code inside the for block, as we did with if Elif, and else statements. We can also iterate over a string, let's write the code and then we will test it. We can also run the code in the Python interpreter. But let's get used to using Python scripts and rewrite our code for now. Okay, so this is the code for iterating over a string.

It is very similar Actually, let's save the file and run the code again. So using a for statement, we assigned each character in the string to a temporary variable called letter. And each time we do this, Python executes the indented code block below the for statement. This means that for each letter in Cisco, Python prints out the letter itself, the same letter doubled and then tripled. And that's how we got this result right here. Next, it's time to see how to use a for loop to iterate over a range.

Remember, we discussed the range data type earlier in the course, that can be used to generate an iterator over which we can iterate and then extract some values. Let's get into the Python interpreter. And first let's create our range r equals range of 10. Now let's use a for loop to iterate over this range. So for i in R, and turn, the indentation is done automatically inside the Python interpreter. Print.

Let's say I times two after hitting Enter twice, we get the result you can see on the screen, which is actually each integer from zero to nine multiplied by two. So what we did is we use the for loop to iterate over the range created by the range function. And for each element in the range, we printed out its value multiplied by two. Nice. Now let's see a more common use of the range function inside the for statement. What if we want to iterate over a list using list indexes?

What do I mean by that? Let's consider the list from earlier. Now we'll remember the Len function we previously used inside the course let's apply it to our list. So Len of vendors equals five. We also know that range of five returns the integers starting at zero up to but not including five, right? Moreover, we can convert this range to a list using the list function.

So let's do this list of range of five we can look Add the elements of this list as being the indexes of each element of our list vendors. So the element Cisco would be positioned at index zero, hp at index one, Nortel at index two, and so on. This means that if we want to get a list of indexes to iterate over using a for loop, we can use range of Len of vendors to obtain that list. I will explain this shortly for now, to use this in practice, let's create a for loop that prints out each element of the vendors list by its index. For this we are going to write the following for element index in a range of Len of vendors, colon, print vendors, and in between square brackets, and index. Don't forget to close the parentheses and this is the result we got so what We did here is we pass the result of one function, Len to another function range.

The result is a range consisting of all the indexes in the vendors list. We then assigned each index in this range to the element index temporary variable, and executed a piece of code for each index. In translation, we told Python to check the length of the vendors list. Then we created a range using that length as an argument for the range function. Finally, Python prints out each element by its index. So we have vendors of zero then vendors of one vendors have two and so on until the list is exhausted.

Another very useful way to iterate over a sequence is by using both the index and the element value as iterating variables. This can be achieved using the enumerate function in Python. So let's see this for index comma element in enumerate of vendors colon print, let's say index comma element. Let's hit enter and see the result first. So using this method, Python returns both the index and the element value at the same time using the enumerate function that helps us iterate over a sequence both by the index and by the element value itself. The last thing I'll add here is that you can also use an else statement for a for loop.

The indented code below else will be executed only when the for loop has finished iterating over the entire sequence. Let's write this code inside the file and then paste it into the Python interpreter. We have four elements in vendors hit tab for the first level of indentation, print element. Next else should be at the same indentation level as four. So we should decrease the indentation now, else, colon. Now again, indented.

In our code, print, and let's say the end of the list has been reached. Okay, let's copy and paste this code right into the Python interpreter. Hit enter. And as you can see, Python printed out each element in vendors. And then when the for loop has finished iterating over the entire list, it executed the code indented below the else statement, resulting in this string right here. Okay, so that's about all you have to know in practice when working with for loops.

You will use them widely across your applications. So you should have a very good understanding of them before moving to more advanced Python concepts.