How to Use Strings in Python - Python Tutorial for Beginners

so here we have this course variable set to Python programming as I told you before whenever you work with text you should surround your text with quotes you can either use double quotes or single quotes that's more of a personal preference but quite often we use double quotes you also have triple quotes and we use them to format a long string for example if you have let's say a variable message that is the message we want to include in the body of an email you can use triple quotes to format it like this hi John this is Marsh from code with marsh comm blah blah blah so that's when we use triple quotes now we don't need this in this lecture so delete let me show you a few useful things you can do with strings first of all we have this built-in function in Python for getting the lengths of strings what is a function a function is basically a reusable piece of code that carries out a task as a metaphor think of the remote control of your TV on this remote control you have buttons for different functions like turn on turn off change the channel and so on these are the built-in functions in your TV in Python and many other programming languages we have the exact same concept so we have functions that are built into the language on the platform you can reuse these functions to perform various tasks so here we can use the built-in Len function to get the length of a string which means the number of characters in that string now whenever you want to use a function you should use parentheses now we say you're calling this function which basically means we are using this function now some functions take additional data which we refer to as arguments these arguments are inputs to these functions so this Len function takes an input or an argument here we pass our course variable and this will return the number of characters in this string so let's print that and see what we get run the program we get 18 because we have 18 characters here let's look at another example if you want to get access to a specific character in this string you use the square bracket notation so here we add course square brackets to get the first character you use the index 0 so in Python like many other languages strings are 0 index which means the index of the first actor or the first element is zero so now when we print this we'll get P okay now you can also use a negative index like minus one what does that mean well if zero represents the first character here what do you think negative one represents that takes us back to the end of this string so that returns the first character from the end of this string let's run this program you will see it will get G there you go using a similar syntax you can slice strings let me show you so I'm gonna duplicate this line and remove negative one now let's say we want to extract the first string characters in this string so here we need two indexes the start index colon the end index so this will return a new string that contains the first three characters in this course variable that will be P Y and T so the index of these characters are 0 1 & 2 so that means the character at the end index is not included ok let's run the program and make sure we get the right result there you go py T now what if we don't include the end index what do you think we're gonna get it's common sense we start from index 0 and go all the way to the end of this string so this will return a new string that is exactly the same as the original string let's take a look so we get python programming now what if we don't include the start index but include the end index what do you think we're gonna get once again it's common sense so by default Python will put 0 here so it will start from the beginning of this string so when I run this program we should get py t one more time there you go and finally as the last example if we don't include the start and the end index this will return a copy of the original string let's look at this so we get Python programming now you don't have to memorize any of these just remember we use the Len function to get the length of a string we use bracket notation to get access to a specific element or a specific character and we use this notation to a slice a string so we have this string here Python programming now let's say we want to put a double quote in the middle of this string there is a problem here Python interpreter sees this second string as the end of the string so the rest of the code is meaningless and invalid how do you solve this problem well there are two ways one way is to use single quotes for our string and then we can use a double quote in the middle of this string but what if for whatever reason perhaps for being consistent in our code we decided to use double quotes how can we add another double quote in the middle of this string well we can prefix this with a backslash backslash in Python strings is a special character we have a jargon for that called escape character we use it to escape the character after let me show you what I mean so let's print this course and run this program what's going on here we don't have the backslash because we use that to escape this double code and basically displayed here so backslash is an escape character and backslash double quote is an escape sequence in Python strings we have a few other escape sequences that you should be aware of let me show you so in Python we use a high sign to indicate a comment a comment is like additional note that we add to our program it's not executed by Python interpreter okay so here are the escape sequences you have seen backslash double quote we also have backslash single quote so we can use that to add a single code here let's run the program here it is beautiful we also have double backslash so if you want to include a backslash in your strings you should prefix it with another backslash let me show you so when we run this we get python one backslash programming and finally we have backslash n which is short for newline so now if I add a backslash n here see what we get we get a new line after Python so programming will end up on the second line so these are the escape sequences in Python here we have two variables first and last let's say we want to print my full name on the console so we can define another variable full set it to first then concatenate it with a space and one more time concatenate it with last now when we print full we get my full name on the console beautiful now this approach are using concatenation to build a string is okay but there is a better and newer approach we can use formatted strings so here we can set full to this string and prefix it with an F which can be lowercase or uppercase this formatted string doesn't have a constant value like these two strings here it's actually an expression that will be evaluated at runtime so here we want to add our first name we use curly braces to print the value of the first variable after that we had a space and then we add curly braces one more time to print the last name so at runtime this expression will be evaluated what we have in between curly braces will be replaced at runtime now let's run this program one more time we get the exact same result just be aware that you can put any valid expressions in between curly braces so earlier you learned about the built-in Len function we can call Len here to get the length of this string let's run this program one more time so we get four we can also replace last with an expression like there's two plus two let's run this program we get four and four so when using formatted strings you can put any valid expressions in between curly braces in this lecture we're going to look at a few useful functions available to work with strings so earlier you learned about this built-in Len function this function is general-purpose so it's not limited to strings later I will show you how to use this function with other kind of objects but in Python we have quite a few functions that are specific to strings let me show you so here if we type course dot C all these are functions available on strings now in precise terms we refer to these functions as methods this is a term in object-oriented programming that you will learn about later in the course for now what I want you to take away is that everything in Python is an object and objects have functions we call methods that we can access using the dot notation so here course is an object we use the dot notation to access its functions or more accurately methods let's take a look at a few of these methods we have upper to convert a string to uppercase now let's print this and run the program here is what we get beautiful now note that the metals that you call here return a new string so the original string is not affected let me show you so print course run the program one more time look this is our original string right so course the upper returns a new string a new value we can store it in a variable like chorus underline capital like this now to keep this demo simple and consistent I'm gonna revert this back and use a print statement we also have the lower method to convert a string to lowercase we also have title which will capitalize the first letter of every word so if our string was like this when we call the title method we get Python programming as you see here okay another useful method is strip and we use it to trim any white space at the beginning or end of a string this is particularly useful when we receive input from the user let me show you so let's imagine the user entered a couple of white spaces at the beginning of this string when we call course that strip those white spaces will be removed take a look so note that in the first three examples we have those white spaces but in the last one it is removed so a strip removed the whitespace from both the beginning and end of a string we also have L strip which is short for left strip and our strip which is short for right strip so it will remove the white space from the end of a string if you want to get the index of a character or a sequence of characters in your string you should use the find method & masaya so course that find so as an argument here we pass another string we can pass a character or a series of characters let's find the index of Pro run the program so the index of Pro is 9 so if you start from 0 here all the way to 9 this is the index of Pro ok now as I told you before python is a case sensitive language so if I pass a capital P here obviously we don't have these exact characters in our string so let's see what we get we get negative 1 that means this string was not found in the original string another useful method is replace so we call replace with this we can replace a character or a sequence of characters with something else so let's say we want to replace all lowercase peas with J with this we get Jai Thunderer cramming whatever that means and finally if you want to check for the existence of a character or a sequence of characters in your string you can use the in operator let me show you so print rewrite an expression like this throw in course so this is an expression as I told you before an expression is a piece of code that produces a value so this expression checks to see if we have Pro in course the difference between this expression and calling the find method is that the find method returns the index of these characters in our string but as this expression returns a boolean so it's a true or false let me show you so run the program we get the boolean true and finally we have the not operator and we use that to see if our string does not contain a character or sequence of characters so let's change this to swift not in course when this expression is evaluated what do you think we're gonna get well we don't have Swift in this string so not in will return true let's take a look there you go so these are the useful string methods next we'll look at numbers hi guys thank you for watching this tutorial my name is muhammad 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 tutorial for beginners, python basics, python for absolute beginners, python strings, learn python, python string slicing, python string, absolute beginners, python tutorial, python 3, python for beginners, getting started with python, programming tutorial, python (programming language), python string methods, learn python online, python 3 tutorial, python data types, python tutorials, string, python for data science

Id: Ctqi5Y4X-jA

Length: 16min 45sec (1005 seconds)

Published: Fri Nov 09 2018