do while and while) you run at a risk. rev2023.7.27.43548. while True means loop forever. I came across a function, in the cs50 module, using a while loop (to keep prompting for an int), where there is no break. You can also specify multiple break statements in a loop: In cases like this, where there are multiple reasons to end the loop, it is often cleaner to break out from several different locations, rather than try to specify all the termination conditions in the loop header. What is the cardinality of intervals in space, and what is the cardinality of intervals in spacetime? Python While Loop Tutorial - Do While True Example Statement Why is "break" in so many languages if it's "not really acceptable"? Note : in the last example, the programmer can obfuscate (willingly or not) the code by mixing the "loop_prepare" with the first "action_A", and action_B with the second action_A. send a video file once and multiple users stream it? while (true) { //do something if (<some condition>) { break; } } Another programmer told me that this was bad practice and that I should replace it with the more standard: while (!<some condition>) { //do something } His reasoning was that you could "forget the break" too easily and have an endless loop. (Loops with continue are usually harder to understand than loops with break.) It may seem as if the meaning of the word else doesnt quite fit the while loop as well as it does the if statement. Execution jumps to the top of the loop, and the controlling expression is re-evaluated to determine whether the loop will execute again or terminate. The "inner" issue is that we're guaranteed that the action following point 1 will be legal, so while reading the code at point 2 I can think about what is being done with a char value I know has been legally obtained. Infinite loops can be very useful. Id use a while(true) loop if I was writing a daemon or other process that should run until it gets killed. Of course the net effect of a1 may invalidate c1, requiring that I think harder about what I can count on at point 2, etc. The while keyword takes an expression, and loops while the expression is true. You use whatever works in the context of your code, if there are multiple options you choose whatever your personal preference is. Trouble understand 'While True' Python robbyweeds August 9, 2022, 6:50pm 1 i was looking throught the PySimpleGUI docs and i saw something i have seen a few times bfore in other Python code. is there a limit of speed cops can go on a high speed pursuit? There are limited situations where a try/except with a pass are used.. not ideal, I agree. Number is 1! If you want some evidence or authority to cite, look no further than Don Knuth's famous paper on Structured Programming with Goto Statements; you will find all the examples, arguments, and explanations you could want. Why is an arrow pointing through a glass of water only flipped vertically but not horizontally? The while True format is more pythonic since you know that break is breaking the loop at that exact point, whereas do_next = False could do more stuff before the next evaluation of do_next. Why did Dick Stensland laugh in this scene? By clicking Post Your Answer, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct. WW1 soldier in WW2 : how would he get caught? Can a judge or prosecutor be compelled to testify in a criminal trial in which they officiated? Well, the bad news is that Python doesnt have a do-while construct. Most languages you're likely to encounter have equivalent idioms. It returns a None, if the user response can't be read. For What Kinds Of Problems is Quantile Regression Useful? rev2023.7.27.43548. If there is a need for multiple exit condition, I tend to refactor the condition determining logic into a separate function so that the loop block looks clean and easier to understand. Now observe the difference here: This loop is terminated prematurely with break, so the else clause isnt executed. Learn Python flow control to understand how you break out of while True loops. In response to your friend's worry of "forget the break", I often write in the following form: By good indentation, the break point is clear to first time reader of the code, look as structural as codes which break at the beginning or bottom of a loop. What mathematical topics are important for succeeding in an undergrad PDE course? To learn more, see our tips on writing great answers. In that case, use: I think the benefit of using "while(true)" is probably to let multiple exit condition easier to write especially if these exit condition has to appear in different location within the code block. Python While Loop | While True and While Else in Python || ToolsQA Just like avoid multiple return statements in a function. This gives me neither an explicit context for reading the body, nor an expectation of what constitutes progress toward (uncertain) termination. The pass is just a way to ignore the error and continue prompting the user for input. How do I check whether a file exists without exceptions? I reckon saying 'while true' is shorthand, but for what? Do the 2.5th and 97.5th percentile of the theoretical sampling distribution of a statistic always contain the true population parameter? Thus, you can specify a while loop all on one line as above, and you write an if statement on one line: Remember that PEP 8 discourages multiple statements on one line. I think it's more appropriate to say 'indefinite loop;' the assumption must be that the loop will be interrupted by a break or return at some point. Afterwards, we define what happens when something goes wrong within the except. Since True always evaluates to True, the loop will run indefinitely, until something within the loop returns or breaks. Then just reset the counter if it doesn't occur continuously: in the. This is denoted with indentation, just as in an if statement. 594), Stack Overflow at WeAreDevelopers World Congress in Berlin, Temporary policy: Generative AI (e.g., ChatGPT) is banned, Preview of Search and Question-Asking Powered by GenAI, I want to print something only once in a while loop in python, Pause an infinite while loop with a single keypress, Relatively new to programming and can't figure out how to exit the magic8ball function back to the gamer function. Execution returns to the top of the loop, the condition is re-evaluated, and it is still true. Once all the items have been removed with the .pop() method and the list is empty, a is false, and the loop terminates. By clicking Post Your Answer, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct. See Structured Programing With Goto Statements by Donald Knuth for some examples. Not the answer you're looking for? while while while while while . The program goes from 1 upwards to infinity and doesn't break or exit the while loop. The Journey of an Electromagnetic Wave Exiting a Router, Epistemic circularity and skepticism about reason. Therefore, having to locate the "breaks" first is a bit troublesome for me. Know what your language considers to be True and False for different operations and flow control to avoid many headaches later! It first evaluates the expression 6 > 5 which is true so is the same as saying while(true). Avoiding the break statement in loop, IMHO, makes code more readable. True will always be True. 594), Stack Overflow at WeAreDevelopers World Congress in Berlin, Temporary policy: Generative AI (e.g., ChatGPT) is banned, Preview of Search and Question-Asking Powered by GenAI, a simple "Hello" prints like "hellohellohellohello" in python socket, While loops in Python 3 and True/False conditions. while True: # Do something and if wanting wanting to break out of loop, break The first three methods are more explicit, so why are they (or one of them) not preferred over the fourth method? multiple conditions which get out of the loop. Then a for statement constructs the loop as long as the variable number is less than 10.. Python allows an optional else clause at the end of a while loop. Can I use the door leading from Vatican museum to St. Peter's Basilica? To learn more, see our tips on writing great answers. Why do code answers tend to be given in Python when no language is specified in the prompt? Is it bad form to use a while loop that will always execute once just to use break statements? So he can have the feeling he is not doing this. You can learn more why this is by reading more about boolean logic. What do multiple contact ratings on a relay represent? I think that forgetting the break is a rather weak argument, as that would be a bug and you'd find and fix it right away. Python While Loop with Break - Examples - Tutorial Kart However, if the loop stops when the condition changes inside the loop, it's more convenient to have the exit point explicitly marked with break, instead of waiting for it to happen on the next iteration of the loop: As was already mentioned in a few other answers, the less code you have to keep in your head while reading a particular line, the better. New! August 9, 2021 by Bijay Kumar In this Python tutorial, we will discuss the Python While loop continue. To learn more, see our tips on writing great answers. As you said, if the last three errors are the same, I want to break it. The loop wont break even if lives == 0, because this condition is tested as part of the loop block, not as the loop condition. I also don't really see the point. Syntax for a single-line while loop in Bash, Iterating over dictionaries using 'for' loops, How to loop through a plain JavaScript object with the objects as members. @adamse In python it is not, however in many languages it is. The reason is that whenever I look back at the code written previously, I usually find that I need to figure out when it runs/terminates more than what it actually does. while True if break while True: s = input(' : ') if s == 'stop': break print(s.capitalize()) # : abc # Abc # : stop continue continue Python: Break vs fulfilling while loop condition? Are there any differences between the first three ways of writing the "while flag == False"? Making statements based on opinion; back them up with references or personal experience. The more the code tells me explicitly, the less complex. Almost there! What is Mathematica's equivalent to Maple's collect with distributed option? The format of a rudimentary while loop is shown below: represents the block to be repeatedly executed, often referred to as the body of the loop. Introduction to the Python break statement. Sometime you need infinite loop, for example listening on port or waiting for connection. "Sibi quisque nunc nominet eos quibus scit et vinum male credi et sermonem bene". Are there any differences between the first three ways of writing the "while flag == False"? How can I delete a file or folder in Python? True is an expression that is always true. Do break operators turn while loop conditions from True to False? Understanding the preconditions of an action are very valuable information when trying to think about what the action accomplishes! Mutables are any object that can be modified, and include dicts, lists. Also, The command "break" will cause the loop to terminate. When that condition becomes false, the loop will break, and the regular flow of code will resume. (with no additional restrictions), Can I board a train without a valid ticket if I have a Rail Travel Voucher, The Journey of an Electromagnetic Wave Exiting a Router. The controlling expression, , typically involves one or more variables that are initialized prior to starting the loop and then modified somewhere in the loop body. Note that most languages usually have some mechanism for breaking out of the loop early. How they work behind the scenes. Truly 'infinite' loops are programmer error; 'indefinite loops' are created by design. Can you have ChatGPT 4 "explain" how it generated an answer? Take the Quiz: Test your knowledge with our interactive Python "while" Loops quiz. You could also rewrite the above Python code to this and it would do the same thing: import random. Sci fi story where a woman demonstrating a knife with a safety feature cuts herself when the safety is turned off. Sometimes, you want to terminate a for loop or a while loop prematurely regardless of the results of the conditional tests. If there is an optional else statement in while or for loop it skips the optional clause also. To answer your question directly: while the loop condition is True. It is a state where the opposite is always False. Secondly, Python provides built-in ways to search for an item in a list. Edit: I just realised you said while true send a video file once and multiple users stream it? Heres another variant of the loop shown above that successively removes items from a list using .pop() until it is empty: When a becomes empty, not a becomes true, and the break statement exits the loop. Well, the simplest true conditional is True itself! Breaking Out of Loops and Blocks | Flow of Control in Python | Peachpit When there is no action_A you can replace it by : When there is no action_B you can replace it by : In the general case, action_A will be executed n times and action_B will be executed (n-1) times. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, The future of collective knowledge sharing. I'm leaving that last point as an exercise for the reader. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, The future of collective knowledge sharing, Your try-catch statement redundant because you can find only integer number with this regular expression. It may be more straightforward to terminate a loop based on conditions recognized within the loop body, rather than on a condition evaluated at the top. If you do any embedded systems programming (think microcontrollers like PICs, MSP430, and DSP programming) then almost all your code will be in a while(1) loop. In Python bietet Ihnen die break -Anweisung die Mglichkeit, eine Schleife zu verlassen, wenn eine externe Bedingung ausgelst wird. This is because bool(0) == False, and 0 == False, but 0 is not False. Readability is a perfectly good reason to do it, too. you can change. But if you can avoid it, you should, because programming should be about writing very complex things in the most obvious way possible, while also implementing features correctly and performantly. while loop in Python (infinite loop, etc.) | note.nkmk.me Many foo output lines have been removed and replaced by the vertical ellipsis in the output shown. What is the least number of concerts needed to be scheduled in order that each musician may listen, as part of the audience, to every other musician? How to initialize an array to a non-numeric value, For loop between two numbers where direction is unknown. First of all, lists are usually processed with definite iteration, not a while loop. How can I remove a key from a Python dictionary? This makes it easier to reason about the state of the program after the loop terminates. No need to convert your already integer value to an integer again and again and AGAIN: Avoid using sys.exit(), you may just break instead (to get out of the loop and continue. If you are writing in C or C++, the preferred idiom is. What should I do to break if the same error occurs three times in a row? So I've fixed your code by replacing the break statement by a return statement. Simply place it under whatever conditional you want to cause the loop to end. Degree. For strs, floats and ints, always check x == b and not x is b. Python break statement: break for loops and while loops Python's statement allows you to exit the nearest enclosing while or for loop. The while-loop condition is simply True, which means it will loop forever unless break is executed. It is not a state but a comparison of opposite states. Is the DC-6 Supercharged? thanks for your comment,i just about half known about while loop..so dont really know how to ask a good question.. Is the DC-6 Supercharged? The British equivalent of "X objects in a trenchcoat". In the case of many break points I would replace them with. Thus, 2 isnt printed. @Lotte, for clarity and also for more practical reason of debugging code. What your friend recommend is different from what you did. How do I make a flat list out of a list of lists? However, for readability and understanding program flow, the while(condition) is better. Instead of this: The is operator tests object identity, which is something quite different from equality. Before we start writing code, let's look at the flowchart to see how it works. Python "while" Loops (Indefinite Iteration) - Real Python While the first three are more explicit, the last one is more readable and clear. You are not testing for a final condition, you are saying "while true:". If you have to use a while true then use an if statement to check if i >=3 and then use a break statement to exit the loop if that's true In this example, it could be easily recoded without a try/except. The Python while loop takes the following form: while EXPRESSION: STATEMENT(S) The while statement starts with the while keyword, followed by the conditional expression. while True mean infinite loop, this usually use by long process. And what if the variable 'hand' is not being assigned a value? Once either of the return statements are executed, the loop will break. For clarity sake I believe you can do while(true == true) in most languages. rev2023.7.27.43548. If you accept any value other than None, check x is None. A 9 speed quicklink fits an 8 speed chain, and feels secure, but is it? rev2023.7.27.43548. In short, I'm with your colleague in the simplest case, but while(true){ } is not uncommon. You just declare a variable outside your loop and initialize to 0, increment it by one each time the loop iterates, and your while loop iterates while it's less than 3. Connect and share knowledge within a single location that is structured and easy to search. for loops, on the other hand, repeat a block of code a fixed number of times. You are not testing for a final condition, you are saying "while true:". For example, you might write code for a service that starts up and runs forever accepting service requests. If you loop over an external condition (not being changed inside the loop), you use while(t), where t is the condition. I think the while True: syntax is fine for simple logic. while loops continue to loop until the condition is false. Pythonwhilebreak What they are used for. You should put your result in a variable (for instance called result) and return it at the end. But there are times breaks are perfectly okay, as mentioned by others. Checking None vs. Other Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, The future of collective knowledge sharing, Am I going to be cast into the role of curmudgeon if I point out the question. Black can also be False until white at which point it is True. So, I suggest that the while (true) idiom is much more incomplete and weak, and therefore more complex, than while (c1) according to the logic I've described above. See the discussion on grouping statements in the previous tutorial to review. We can define an object boolean value by implementing __bool__() function. No spam ever. The first is OK if there are many ways to break from the loop, or if the break condition cannot be expressed easily at the top of the loop (for example, the content of the loop needs to run halfway but the other half must not run, on the last iteration). How common is it for US universities to ask a postdoc to bring their own laptop computer etc.? Help identifying small low-flying aircraft over western US? Making statements based on opinion; back them up with references or personal experience. John is always John. It will break out of the loop and continue the program running. Python while Loop | Linuxize Just remember that you must ensure the loop gets broken out of at some point, so it doesnt truly become infinite. Connect and share knowledge within a single location that is structured and easy to search. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. If the loop is exited by a break statement, the else clause wont be executed. While similar questions may be on-topic here, this one was resolved in a way less likely to help future readers. This is dead code since you have set lives to 5 2 lines above and not modified it afterwards: You should check if the user actually inputs a valid integer convertible value instead of an arbitrary string: (continue will skip to the next loop iteration, so it will ask the user for input again without decrementing lives.