In Python, if a variable is a numeric zero or empty, or a None object then it is considered as False, otherwise True. Python has two primitive loop commands: while loops; for loops; The while Loop. Example. while expression: statement(s) Here, statement(s) may be a single statement or a block of statements. While loops, like the ForLoop, are used for repeating sections of code - but unlike a for loop, the while loop will not run n times, but until a defined condition is no longer met. In spite of being present in most of the popular programming languages, Python does not have a native do-while statement. Python not: If Not TrueApply the not-operator to see if an expression is False. However, do-while will run once, then check the condition for subsequent loops. The condition may be any expression, and true is any non-zero value. dot net perls. There are two ways to write the Python not equal comparison operator:. Usage in Python. Python Program #not boolean value a = False if not a: print('a is false.') The expression not x means if x is True or False. The statements within the while are not reached. In that case, as x = 10 so it is True. After you enter something, you get out of the loop. While loops. Kite is a free autocomplete for Python developers. Invert the value of booleans. With this keyword we change the meaning of expressions. If the condition is initially false, the loop body will not be executed at all. When do I use them? A shadow is the absence of light. A while loop statement in Python programming language repeatedly executes a target statement as long as a given condition is true.. Syntax. Keyword info. Browse other questions tagged python-3.x while-loop range or ask your own question. The Overflow Blog Podcast 300: Welcome to 2021 with Joel Spolsky 发布于 2016-05-21. dot net perls. Python While Loops Previous Next Python Loops. Empty strings in Python are evaluated as false, so the use of 'not' make it true; therefore, you get in the loop, and until you've not entered anything, you're still in the loop. Print i as long as i is less than 6: i = 1 while i 6: print(i) i += 1 Code faster with the Kite plugin for your code editor, featuring Line-of-Code Completions and cloudless processing. A while loop might not even execute once if the condition is not met. The syntax for not equal in Python. Not. So We can use the else-statement, after the main part of a while-loop, to catch these situations. While continues until a terminating condition is met. As x is True, so not operator evaluated as False and else part executed. The syntax of a while loop in Python programming language is −. 学习PYTHON基础教程 看到” while not name:" 这个怎么理解 ... name这个值是空的时候,while才循环运行. Most developers recommend sticking with != in Python, because both Python 2 and Python 3 support this syntax.>, however, is deprecated in Python 3, and only works in older versions: #!/usr/bin/python count = 0 while count < 5: print count, " is less than 5 " count = count + 1 else: print count, " is not less than 5 " 以上实例输出结果为： 0 is less than 5 1 is less than 5 2 is less than 5 3 is less than 5 4 is less than 5 5 is not less than 5 With the while loop we can execute a set of statements as long as a condition is true. Consider the "not" keyword in Python. In this example, we will use Python not logical operator in the boolean expression of Python IF. While. #not boolean condition a = 5 if not a==5: print('a is not 5') else: print('a is 5') Python while Loop ExamplesUnderstand the while-loop. name 是 True, not name 是false name是 False, not name是True.