Tip: A bug is an error in the program that causes incorrect or unexpected results. check out this article recently published on freeCodeCamp. You can add an "else" statement to run if the loop condition fails. Nun meine Frage: Wie … The loop condition is len(nums) < 4, so the loop will run while the length of the list nums is strictly less than 4. 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 table illustrates what happens behind the scenes: Four iterations are completed. 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. Schleifen, werden benötigt, um einen Codeblock, den man auch als Schleifenkörper bezeichnet, wiederholt auszuführen. When the condition evaluates to False, the loop stops and the program continues beyond the loop. Die meisten Schleifen enthalten einen Zähler oder ganz allgemein Variablen, die im Verlauf der Berechnungen innerhalb des Schleifenkörpers ihre Werte ändern. Infinite loops are the ones where the condition is always true. 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? #!/usr/bin/python # coding =utf-8 import spidev import time spi = spidev.SpiDev() spi.open(0,1) while True: antwort = spi.xfer([1,128,0]) if 0 <= antwort[1] <=3: wert = ((antwort[1] * 256) + antwort[2]) * 0.00322 print wert ," V" time.sleep(10) Dieses Programm liest alle 10 Sekunden die Daten von meinen Analog-Digitalwandler aus. Eine + while + Schleife implementiert die wiederholte Ausführung von Code basierend auf einer bestimmten Boolean Bedingung. We also have thousands of freeCodeCamp study groups around the world. A condition to determine if the loop will continue running or not based on its truth value (. One of the popular functions among them is sleep().. Wie Sie die for- und die while-loop in Python richtig benutzen, zeigen wir in diesem Praxistipp. You just need to write code to guarantee that the condition will eventually evaluate to False. Der Code, der sich in einem "+ while" -Block befindet, wird ausgeführt, solange die "+ while" -Anweisung "True" ergibt. In fact, what you will see a lot of in Python is the following: while True: n = raw_input("Please enter 'hello':") if n.strip() == 'hello': break. 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. Syntax. The condition is evaluated to check if it's. そして、条件式がFalseになった時にwhile文は終了します。. Here's how you write a simple while loop to print numbers from 1 to 10. Therefore, the while loop will run every time. There are two variations of the while loop – while and do-While. Dies wird fortgesetzt, solange die Bedingung wahr ist. 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 loop will run indefinitely until an odd integer is entered because that is the only way in which the break statement will be found. This will make the loop run forever. #!/usr/bin/python flag = 1 while (flag): print ' Given flag is really true! ' When x is 11, the while condition will fail, triggering the else condition. 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. Ist die Bedingung nicht erfüllt, wird die Schleife gar nicht durchlaufen. However, you want to continue subsequent executions until the main while condition turns false. There is no command to alter the value of x, so the condition "x is greater than or equal to 1" is always true. Eine while … freeCodeCamp's open source curriculum has helped more than 40,000 people get jobs as developers. Let's start with the purpose of while loops. Finally, let's look at how to control the flow of a loop while it is running. Having True as a condition ensures that the code runs until it's broken by n.strip() equaling 'hello'. Tweet a thanks, Learn to code for free. Always be careful while writing loops. Now you know how to work with While Loops in Python. Donations to freeCodeCamp go toward our education initiatives, and help pay for servers, services, and staff. Before we start writing code, let's look at the flowchart to see how it works. while True means loop forever. This block of code is called the "body" of the loop and it has to be indented. There are two major types of loops in Python. 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。. 図解！. Before we start writing code, let's look at the flowchart to see how it works. In this article, we will look at while loops in Python. You can use the "continue" keyword for that, like this: In the above example,  the loop will print from 1 to 10, except 5. If a statement is not indented, it will not be considered part of the loop (please see the diagram below). If you liked this article, you can read my blog here. Let's look at how while loops work in Python. The process starts when a while loop is found during the execution of the program. If it is, the message This number is odd is printed and the break statement stops the loop immediately. 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. This value is used to check the condition before the next iteration starts. Both these types of loops can be used for similar actions. The while loop will check the condition every time, and if it returns "true" it will execute the instructions within the 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. The while statement takes an expression and executes the loop body while the expression evaluates to (boolean) "true". This input is converted to an integer and assigned to the variable user_input. in einem Shop 20 Artikel ausgeben lassen. To learn more about for loops, check out this article recently published on freeCodeCamp. 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。 Tip: You can (in theory) write a break statement anywhere in the body of the loop. 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. The condition is checked again before starting a "fifth" iteration. Python while loop is a conditional statement that runs as long as an expression evaluates to true. 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!" While Loop. Die while-Schleife läuft 10-mal und gibt dann 10 Artikel aus. Loops help you execute a sequence of instructions until a condition is satisfied. 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. Now you know how while loops work, but what do you think will happen if the while loop condition never evaluates to False? This diagram illustrates the basic logic of the break statement: This is the basic logic of the break statement: We can use break to stop a while loop when a condition is met at a particular point of its execution, so you will typically find it within a conditional statement, like this: This stops the loop immediately if the condition is True. We also have thousands of freeCodeCamp study groups around the world. Better still, we can simply omit the condition altogether to ensure that the while true loop never ends. We can generate an infinite loop intentionally using while True. What infinite loops are and how to interrupt them. Python has a module named time which provides several useful functions to handle time-related tasks. We have to update their values explicitly with our code to make sure that the loop will eventually stop when the condition evaluates to False. Before you start working with while loops, you should know that the loop condition plays a central role in the functionality and output of a while loop. However, do-while will run once, then check the condition for subsequent loops. You must be very careful with the comparison operator that you choose because this is a very common source of bugs. Geben Sie eine ganze Zahl ein: 23 Glueckwunsch, Sie haben es erraten. Else, if the input is even , the message This number is even is printed and the loop starts again. A while loop statement in Python programming language repeatedly executes a target statement as long as a given condition is true. When the condition becomes false, program control passes to the line immediately following the loop. Therefore, the condition i < 15 is always True and the loop never stops. The loop runs until CTRL + C is pressed, but Python also has a break statement that we can use directly in our code to stop this type of loop. If the Condition is False then compiler will come out of the loop and execute other statements outside the while loop. This statement is used to stop a loop immediately. 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 … If you are learning to code, loops are one of the main concepts you should understand. The above code is an example of an infinite loop. Donations to freeCodeCamp go toward our education initiatives, and help pay for servers, services, and staff. The while loop condition is checked again. Wenn die Bedingung True ist, wird der Schleifenkörper ausgeführt, und dann wird die Bedingung erneut überprüft. Computer Science and Mathematics Student | Udemy Instructor | Author at freeCodeCamp News, If you read this far, tweet to the author to show them you care. 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. A “do while” loop is called a while loop in Python. The expression in the while statement header on line 2 is n > 0, which is true, so the loop body executes. Vor jedem Schleifendurchlauf wird geprüft, ob ein Ausdruck, in dem … Get started, freeCodeCamp is a donor-supported tax-exempt 501(c)(3) nonprofit organization (United States Federal Tax Identification Number: 82-0779546). If the condition is True, the statements that belong to the loop are executed. What are they used for? Dazu sollten Sie sich jedoch zunächst unseren Artikel zum Thema "Bedingungen" durchlesen. messages because the body of the loop print("Hello, World!") 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. (if, break, continue, inputとの組合せなど) while文とは、繰り返し処理の1つで、指定された条件式がTrueの間は処理が繰り返し実行されます。. This is the basic syntax: Tip: The Python style guide (PEP 8) recommends using 4 spaces per indentation level. This feature is referred to as loops. 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. So funktioniert es. You will learn how while loops work behind the scenes with examples, tables, and diagrams. The sequence of statements that will be repeated. 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.