This block of code is called the "body" of the loop and it has to be indented. You will learn how while loops work behind the scenes with examples, tables, and diagrams. Before a "ninth" iteration starts, the condition is checked again but now it evaluates to False because the nums list has four elements (length 4), so the loop stops. When x is 11, the while condition will fail, triggering the else condition. Geben Sie eine ganze Zahl ein: 22 Nein, die Zahl ist etwas hoeher. $ python while.py Geben Sie eine ganze Zahl ein: 50 Nein, die Zahl ist etwas niedriger. First compiler will check the condition inside the Python While loop. When we write a while loop, we don't explicitly define how many iterations will be completed, we only write the condition that has to be True to continue the process and False to stop it. Geben Sie eine ganze Zahl ein: 23 Glueckwunsch, Sie haben es erraten. If we check the value of the nums list when the process has been completed, we see this: Exactly what we expected, the while loop stopped when the condition len(nums) < 4 evaluated to False. We accomplish this by creating thousands of videos, articles, and interactive coding lessons - all freely available to the public. You should think of it as a red "stop sign" that you can use in your code to have more control over the behavior of the loop. The code works once even though I have it set in a loop, what do I need to change to make it work. Loops are one of the most useful components in programming that you will use on a daily basis. check out this article recently published on freeCodeCamp. While True → Loop will run forever unless we stop it because the condition of while is always True.. We can stop it using break statement. This input is converted to an integer and assigned to the variable user_input. Therefore, the condition i < 15 is always True and the loop never stops. You can make a tax-deductible donation here. If the condition evaluates to True again, the sequence of statements runs again and the process is repeated. Wie Sie die for- und die while-loop in Python richtig benutzen, zeigen wir in diesem Praxistipp. You can use the "continue" keyword for that, like this: In the above example,  the loop will print from 1 to 10, except 5. Eine while … The Python syntax for while loops is while[condition]. If you liked this article, you can read my blog here. Donations to freeCodeCamp go toward our education initiatives, and help pay for servers, services, and staff. If the Condition is True then the statement or group of statements under the while loop block will be executed. Here's another scenario: say you want to skip the loop if a certain condition is met. Let's look at how while loops work in Python. messages because the body of the loop print("Hello, World!") However, you want to continue subsequent executions until the main while condition turns false. While loops are very powerful programming structures that you can use in your programs to repeat a sequence of statements. Loops help you execute a sequence of instructions until a condition is satisfied. Wie sieht eine while-Schleife in Python aus? Always be careful while writing loops. It's an idiom that you'll just get used to eventually! Remember that while loops don't update variables automatically (we are in charge of doing that explicitly with our code). Eine While-Schleife ist eine Schleife mit vorangestellter Bedingung. Always be aware of creating infinite loops accidentally. A while loop might not even execute once if the condition is not met. In this article, we will look at while loops in Python. The process starts when a while loop is found during the execution of the program. Making tech easier for people, one article at a time. freeCodeCamp's open source curriculum has helped more than 40,000 people get jobs as developers. while True means loop forever. For and while are the two main loops in Python. So there is no guarantee that the loop will stop unless we write the necessary code to make the condition False at some point during the execution of the loop. while True 是python中经常会被应用到。下面通过个例子进行解释： 下面是阿里云的子账户登陆界面，在输入账户时候会要求，账户名称内必须包含 ’ @ ‘，否者认为是无效账户，并提示要重新输入账户。 Instead of writing a condition after the while keyword, we just write the truth value directly to indicate that the condition will always be True. Most programming languages include a useful feature to help you automate repetitive tasks. Wenn die Bedingung True ist, wird der Schleifenkörper ausgeführt, und dann wird die Bedingung erneut überprüft. To learn more about for loops, check out this article recently published on freeCodeCamp. This type of loop runs while a given condition is True and it only stops when the condition becomes False. Inside the loop body on line 3, n is decremented by 1 to 4, and then printed. while-Schleife in Python. As you can see, this compacts the whole thing into a piece of code managed entirely by the while loop. 図解！. The syntax of a while loop in Python programming language is − while expression: statement(s) Here, statement(s) may be a single statement or a block of statements. While the loop is skipped if the initial test returns FALSE, it is also forever repeated infinitely if the expression always returns TRUE.. For example, while loop in the following code will never exit out of the loop and the while loop will iterate forever. Infinite loops are typically the result of a bug, but they can also be caused intentionally when we want to repeat a sequence of statements indefinitely until a break statement is found. When you are writing real world applications, you will often encounter scenarios where you need to add additional conditions to skip a loop or to break out of a loop. Tip: if the while loop condition never evaluates to False, then we will have an infinite loop, which is a loop that never stops (in theory) without external intervention. If we don't do this and the condition always evaluates to True, then we will have an infinite loop, which is a while loop that runs indefinitely (in theory). Here's how you write a simple while loop to print numbers from 1 to 10. Welcome! If while loop expression always evaluates to true. In order to make that sequence of code run in an infinite loop, we can set the condition to be one that is impossible to reach. Before starting the fifth iteration, the value of, We start by defining an empty list and assigning it to a variable called, Then, we define a while loop that will run while. The expression in the while statement header on line 2 is n > 0, which is true, so the loop body executes. The loop iterates while the condition is true. But as you learn to write efficient programs, you will know when to use what. Die meisten Schleifen enthalten einen Zähler oder ganz allgemein Variablen, die im Verlauf der Berechnungen innerhalb des Schleifenkörpers ihre Werte ändern. You must be very careful with the comparison operator that you choose because this is a very common source of bugs. This can affect the number of iterations of the loop and even its output. Python While Loops Previous Next ... With the break statement we can stop the loop even if the while condition is true: Example. Before we start writing code, let's look at the flowchart to see how it works. Über Schleifen können wir Aktion mehrmals ausführen lassen, bis eine festgelegte Bedingung erfüllt ist. We also have thousands of freeCodeCamp study groups around the world. This statement is used to stop a loop immediately. このwhile文の条件式にTrueを指定すると、無限にループが繰り返されます。. We accomplish this by creating thousands of videos, articles, and interactive coding lessons - all freely available to the public. Before we start writing code, let's look at the flowchart to see how it works. Else, if it's odd, the loop starts again and the condition is checked to determine if the loop should continue or not. Let's see these two types of infinite loops in the examples below. Python while True 無限ループの抜け方と使い方を解説！. Both these types of loops can be used for similar actions. will run indefinitely. Here we have an example with custom user input: I really hope you liked my article and found it helpful. Die while-Schleife wurde beendet. In Python, all the statements indented by the same number of character spaces after a programming construct are considered to be part of a single block of code. Let's add an else condition to our code to print "Done" once we have printed the numbers from 1 to 10. Ist die Bedingung nicht erfüllt, wird die Schleife gar nicht durchlaufen. If we run this code with custom user input, we get the following output: This table summarizes what happens behind the scenes when the code runs: Tip: The initial value of len(nums) is 0 because the list is initially empty. Tip: A bug is an error in the program that causes incorrect or unexpected results. while(条件式): において条件式が True である限りWhileループは実行され続けます。従って、 While(False): と書けば、絶対に実行されないwhileループになります。そして、 While(True): と書けば無限ループになります。 しかし、無限ループでは困るので、While(True):を使 … 8 years of #remotelife. while-Schleife (Python) Beispiel #1 #!/usr/bin/env python print "Content-type: text/html\n\n" x = 0 while x < 10: print x x = x + 1 Beispiel #2 #!/usr/bin/env python print "Content-type: text/html\n\n" x = 0 while x < 10: print x x = x + 1 else: # Wenn die Bedingung das erste mal False ergibt print "Fertig!" freeCodeCamp's open source curriculum has helped more than 40,000 people get jobs as developers. Python 3 - While-Schleife while - Schleife. If you want to learn how to work with while loops in Python, then this article is for you. When x is 5, the rest of the commands are skipped and the control flow returns to the start of the while program. In spite of being present in most of the popular programming languages, Python does not have a native do-while statement. Fertig. You can add an "else" statement to run if the loop condition fails. Python Loops and Looping Techniques: Beginner to Advanced. While Loop. If a statement is not indented, it will not be considered part of the loop (please see the diagram below). Infinite loops are the ones where the condition is always true. 注意： 以上的无限循环你可以使用 CTRL+C 来中断循环。 Python 条件语句 The while statement takes an expression and executes the loop body while the expression evaluates to (boolean) "true". If the condition is True, the statements that belong to the loop are executed. Now let's see an example of a while loop in a program that takes user input. This table illustrates what happens behind the scenes: Four iterations are completed. Learn to code — free 3,000-hour curriculum. If the Condition is False then compiler will come out of the loop and execute other statements outside the while loop. If you are learning to code, loops are one of the main concepts you should understand. The condition may be any expression, and true is any non-zero value. If you are not careful while writing loops, you will create infinite loops. We will the input() function to ask the user to enter an integer and that integer will only be appended to list if it's even. Let’s create a small program that executes a while loop. The loop iterates while the … d = {} while True: name = input('请输入您的用户名：') if name in d: break else: print('您输入的用户名不存在，请重新输入') continue while True: password = input('请输入您的密码：') if d[name] == password: print('进入系统') break else: print('您输入的密码不正确，请重新输入') continue What are they used for? Der Code, der sich in einem "+ while" -Block befindet, wird ausgeführt, solange die "+ while" -Anweisung "True" ergibt. There is no command to alter the value of x, so the condition "x is greater than or equal to 1" is always true. Tip: We need to convert (cast) the value entered by the user to an integer using the int() function before assigning it to the variable because the input() function returns a string (source). There are two major types of loops in Python. Dazu sollten Sie sich jedoch zunächst unseren Artikel zum Thema "Bedingungen" durchlesen. Therefore, the while loop will run every time. Our mission: to help people learn to code for free. To stop the program, we will need to interrupt the loop manually by pressing CTRL + C. When we do, we will see a KeyboardInterrupt error similar to this one: To fix this loop, we will need to update the value of i in the body of the loop to make sure that the condition i < 15 will eventually evaluate to False. The difference between the two is that do-while runs at least once. Die Bedingung wird noch bevor die darauffolgenden Anweisungen in dem Schleifenkörper abgearbeitet werden geprüft. What infinite loops are and how to interrupt them. Dies wird fortgesetzt, solange die Bedingung wahr ist. Finally, let's look at how to control the flow of a loop while it is running. In Python gibt es zwei Schleifentypen: die while-Schleife und die for-Schleife. Wir werden uns in diesem Tutorial mit der * while-Schleife * von Python befassen. Denn Schleifen programmieren ist gar nicht mal so schwer. If it is, the message This number is odd is printed and the break statement stops the loop immediately. Now you know how while loops work, but what do you think will happen if the while loop condition never evaluates to False? The condition is evaluated to check if it's. Das Programm funktionier einwandfrei. An infinite loop is a loop that runs indefinitely and it only stops with external intervention or when a, You can generate an infinite loop intentionally with. True always evaluates to boolean "true" and thus executes the loop body indefinitely. Loops are a sequence of instructions executed until a condition is satisfied. Außerhalb, d.h. noch vor dem Beginn der Schleife, werden diese Variablen initialisiert. Learn to code — free 3,000-hour curriculum. You just need to write code to guarantee that the condition will eventually evaluate to False. This feature is referred to as loops. However, do-while will run once, then check the condition for subsequent loops. Once the while loop starts, the "run_commands" function will never be executed since x is equal to 20. Tip: You can (in theory) write a break statement anywhere in the body of the loop. Now that you know how while loops work and how to write them in Python, let's see how they work behind the scenes with some examples. You can make a tax-deductible donation here. Get started, freeCodeCamp is a donor-supported tax-exempt 501(c)(3) nonprofit organization (United States Federal Tax Identification Number: 82-0779546). while文は「ある条件を満たす間(Trueの間）、指定の処理を繰り返す」というものです。つまり条件が常にTrue（=真）であれば、指定の処理を永遠に繰り返す無限ループになるということです。Pythonでは、そのような無限ループを作りたい時は、次のように「while True」と書きます。 これで常に条件がTrue（=真）となり、下図のような無限ループになります。 ただし、このまま例えば次のようなコードを書くと、0から1ずつ増えていく数値を永遠に出力し続けてしまいます。 この処理の流れは下図の … The while loop condition is checked again. If you initialise x as 20, the loop will never execute. Before the first iteration of the loop, the value of, In the second iteration of the loop, the value of, In the third iteration of the loop, the value of, The condition is checked again before a fourth iteration starts, but now the value of, The while loop starts only if the condition evaluates to, While loops are programming structures used to repeat a sequence of statements while a condition is. This is an example of an unintentional infinite loop caused by a bug in the program: Don't you notice something missing in the body of the loop? The loop completes one more iteration because now we are using the "less than or equal to" operator <= , so the condition is still True when i is equal to 9. We also have thousands of freeCodeCamp study groups around the world. When the condition evaluates to False, the loop stops and the program continues beyond the loop. Else, if the input is even , the message This number is even is printed and the loop starts again. Learn more at https://www.manishmshiva.com, If you read this far, tweet to the author to show them you care. The while loop has two variants, while and do-while, but Python supports only the former. Wenn es False ist, wird die Schleife beendet und die Kontrolle wird nach dem while Schleifenkörper an die nächste Anweisung übergeben. The while loop condition is checked again. Syntax. These are some examples of real use cases of while loops: Now that you know what while loops are used for, let's see their main logic and how they work behind the scenes. import pyautogui, time time.sleep(5) while True: pyautogui.press(e) pyautogui.click() if w or a or s or d: stop() #!/usr/bin/python flag = 1 while (flag): print ' Given flag is really true! ' The last column of the table shows the length of the list at the end of the current iteration. This value is used to check the condition before the next iteration starts. So können wir z.B. When the body of the loop has finished, program execution returns to the top of the loop at line 2, and the expression is evaluated again. The above code is an example of an infinite loop. The sequence of statements that will be repeated. i = 5 while … A ‘while true’ statement allows us to run a sequence of code until a particular condition is met. like an example:-like this, we can use the syntax of while true- There are two variations of the while loop – while and do-While. Better still, we can simply omit the condition altogether to ensure that the while true loop never ends. This table illustrates what happens behind the scenes when the code runs: In this case, we used < as the comparison operator in the condition, but what do you think will happen if we use <= instead? Schleifen, werden benötigt, um einen Codeblock, den man auch als Schleifenkörper bezeichnet, wiederholt auszuführen. Vor jedem Schleifendurchlauf wird geprüft, ob ein Ausdruck, in dem … A “do while” loop is called a while loop in Python. The third line checks if the input is odd. We can generate an infinite loop intentionally using while True. This is one possible solution, incrementing the value of i by 2 on every iteration: Great.