Python For Loops - Python Tutorial for Absolute Beginners

there are times that we may want to repeat a task a number of times for example let's say we send a message to a user if that message cannot be delivered perhaps we want to retry three times now for simplicity let's imagine this print statement is equivalent to sending a message in a real work program to send a message to a user we have to write five to ten lines of code now if you want to retry three times we don't want to repeat all that code that is ugly that's when we use a loop we use loops to create repetition so here is how it works we start with four number in we have a built-in function called range now how many times we want to repeat this task let's say three times so we call range and pass three as an argument now similar to our if statements we need to terminate this line with a colon enter we get indentation so in this block we can write all the statements that should be repeated three times let's do a print a message like attempt save the changes run the program so we have attempt printed three times beautiful now what is this number let's take a look it's a variable of type integer so let's pass it as the second argument to the print function number run the program this is what we get zero one two so here we have a for loop this for loop is executed three times in each iteration number will have a different value initially it will be zero in the second iteration it will be one and finally in the last iteration it will be two now here we can do something fun we can add one to this run the program and now the message is that the print are kind of more meaningful or more user-friendly like attempting number one attempting number two and so on we can take this to the next level so we can pass another argument here I'm going to add an expression one more time number plus one so we'll get one two three now I want to put this expression in parenthesis so let's select this put it in parenthesis and then multiply it by a dot so here we have a string that is multiplied by a number the result will be that string repeated that number of times let's take a look so run the program see that's pretty cool isn't it now let me show you one more thing before you finish this lecture as you saw this range function generates numbers starting from zero all the way up to this number here but it doesn't include this number here we can pass another argument say start from one and finish before four with this change we don't need to add one to number every time because in the first iteration this number variable will be set to one so we can simplify our code and make it cleaner let's run it one more time we get the exact same result we can also pass a third argument as a step so I'm going to change the second argument to ten and pass two as a step look at the result these are the numbers we get 1 3 5 and so on so pretty useful you're going to use this function a lot in real-world applications continuing with the example from the last lecture let's imagine the scenario where after the first attempt we can successfully send the message in that case you want to jump out of this loop we don't want to repeat this task of sending a message three times let me show you how to implement this so in this demo I'm gonna simulate the scenario where we can successfully send a message so we define a variable successful and set it to true now here after this print statement we'll have an if statement if successful : then perhaps we can print successful now here we want to jump out of this loop for that we use the break statement let's run this program and see what happens so there you go after the first attempt we are successful and there are no more attempts so once again I want you to pay great attention to the indentation here because that's one of the common issues amongst beginners so here's our for loop these two lines are indented with four spaces and they belong to our for loop in every iteration these two lines will be executed now when we get to line four if this condition is true then these two lines will be executed because both these lines are indented below this if statement now let's take this program to the next level what if we attempt three times and we still cannot send an email perhaps we want to display a different message to the user we say hey we tried three times but it didn't work so I'm gonna change successful to false now at the end here we can add an else statement this is what we call a for else statement what we put under this else statement will only be executed if this loop completes without an early termination so if we never break out of this loop then the else statement will be executed so here we can print a message like attempt at three times and failed so run the program see what we get three attempts followed by this message attempted three times and failed in contrast if we change successful to true because we terminate this loop using this break statement what we have in the else block will not be executed take a look run the program we have one attempt successful done in programming we have this concept called nested loops so we can put one loop inside of another loop and with this we can get some interesting results let me show you so I'm going to start with this loop for X in range 5 : now inside of this loop I'm gonna add another loop so for Y in range 3 : and then in our second loop I'm gonna add a print statement here we can use formatted strings to display coordinates remember formatted string so we have F followed by quotes now here we add parentheses for our coordinate first we want to display X and then comma followed by Y let's run this program and see what happens there you go pretty cool isn't it so we get 0 + 0 0 1 0 & 2 then we get 1 & 0 1 & 1 1 & 2 and so on now let me explain how exactly Python interpreter executes this code so here we have two loops this is what we call the outer loop and this is the inner loop so the execution of our program starts here in the first iteration of this loop X is 0 now we get to this statement which is a child of this for statement because it's indented four times this statement itself is a loop so what we have inside of this loop will be executed three times in the first iteration X is 0 because we're still in the first iteration of the outer loop and Y is also 0 because we're in the first iteration of the inner loop that is why we get 0 and 0 now we go to the second iteration of this inner loop in this iteration Y will be 1 whereas X is still 0 that is why we get 0 and 1 and similarly in the third iteration of our inner loop we'll get 0 and 2 in now we're done with the execution of the inner loop so the control moves back to our outer loop here we'll be in the second iteration so X will be 1 and then we start here again so we have to execute this inner loop 3 times in the first iteration Y will be 0 and X is 1 so here we have 1 and 0 then we'll get one on one and one and two you got the point so this is all about nested loops so you have learned how to use four loops to repeat one or more statements in your programs now let's dive deeper and see what this range function returns so earlier you learn about the built in type function with this function we can get the type of an object so if I pass five here and run this program this is what we get so the type of this number or this object is int or integer now let's look at the type of the value that we get from the range function so as an argument we pass range of a number let's run this program so this range function returns an object of type range so in Python we have primitive types like numbers strings and boolean but we also have complex types range is an example one of those complex types throughout this course you're going to learn about a lot of other complex types now what is interesting about this range object is that it's iterable which means we can iterate over it or use it in a for loop that is why we can write code like this so this range function returns a range object which is eatable which means we can iterate over it in each iteration X will have a different value now range objects are not the only iterable objects in Python strings are also iterable so here we can add a string like Python now in each iteration X will hold one character in this string let me show you so print Peg's and I'm gonna delete these two lines here let's run this program so in each iteration we'll get one character and print it we have another complex type called list which we use to store a list of objects so we add square brackets this indicates a list now we can add a list of numbers or a list of strings like a list of names you will learn about lists later in the course so let's run this one more time as we can see we can iterate over lists in each iteration we'll get one object in this list now later in the course I will show you how to create your own custom objects that are eatable for example you will learn how to write code like this for item in shopping cart print item so shopping cart is going to be a custom object that you will create it's not going to be an integer or a string or boolean it's a custom object it has a different structure and we'll make it eatable so we can use it in a for loop and in each iteration we can get one item in the shopping cart and print it on a terminal alright time for an exercise I want you to write a program to display the even numbers between 1 to 10 so when you run this program you should see 2 4 6 and 8 and after these I want you to print this message we have 4 even numbers now here is a quick hint before you get started you should call the range function with 1 and 10 do not use the third argument which is called step so basically I want you to iterate over all the numbers between 1 to 10 check if each number is an even number and then print it on the terminal so pause the video spend two minutes on this exercise when you're done come back continue watching so it started with a four loop for a number in range one to ten : we check to see if the remainder of division of this number by two equals zero so if number modulus two equals zero then we print this number now let's run this program so we get two four six eight beautiful now to count the even numbers we need a separate variable so let's call that count initially we set it to zero now in this if block every time we find an even number we need to increment count so we set count plus equals one and finally after our for loop we can print a formatted string we have count even numbers let's run the program and here's the result hi guys thank you for watching this tutorial my name is Mohammad Ani and I have tons of tutorials like this for you on my channel so be sure to subscribe and also please like and share this video if you want to learn Python properly from scratch with depth I have a comprehensive Python tutorial for you the link is below this video so click the link to get started thank you and have a fantastic day

Channel: Programming with Mosh

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Keywords: python loops, control flow, python basics, python (programming language), python 3, learn python, for loops, for loop, python tutorial for beginners, python for beginners, code with mosh, python tutorial, how to, python, programming language, python tutorials, getting started with python, learning python, software development, python language, coding, python tutorials for beginners, programming

Id: 94UHCEmprCY

Length: 14min 41sec (881 seconds)

Published: Mon Nov 05 2018