2023年6月24日发(作者：)

python基础知识（⼆）--判断，循环（is,isnot,not,if,for,while）1.概述只需要掌握is, is not, not, if,for, while的⽤法，就可以很轻松的实现python中所有的判断语句，循环语句。, is not, not在python中 None, False, 空字符串"", 0, 空列表[], 空字典{}, 空元组()都相当于False,可以⽤　is 或者 is not　来准确区分它们a = ""if a is not None: print('not None')if a is not False: print('not false')if a is not {}: print('not {}')如果⽤not来计算的话，他们都是Ｆalseif not a: print("not a")可⽤于字符串，列表元素，字典键值判断。a = "shanghai"my_lists = list(a)my_dic = {"a":1,"b":2,"c":3}print(a)print(my_lists)if "s" in a: print("s in a")if "a" in my_lists: print("a in my list")if "a" in my_dic: print("a in my dic")可实现选择逻辑，三⽬运算#ifa = ""if a is None: print("None")elif a is False: print("False")else: print("else")#三⽬运算print('True') if a is "" else 'False',whilecontinue，这次循环到此结束，开始执⾏下个循环。break，整个循环都结束了。else，是当整个循环都结束后，才执⾏。如果提前结束，则不执⾏。#forfor i in range(10): #continue print(i) if i == 9: breakelse: print('the laste one is :%s'%i)#whilesum10 = 0i = 1while i <= 10: i += 1 #continue sum10 += i #breakelse: print(sum10)