python基础语法 - 循环
while循环
1.基本语法
while 条件: …… if 条件: continue # 条件满足跳过当次循环 if 条件 break # 条件满足中止循环 else: # 只有当while循环结束后,才会执行else下面的语句 ……
ctrl + c 退出循环
2.循环的嵌套
while 条件: …… while 条件: ……
3.示例(使用 # 号 输出一个长方形,用户可以指定宽和高)
length = int(input('please input length:')) heigh = int(input('please input heigh:')) num2 = 0 while num2 < heigh: num1 = 0 while num1 < length: print('#', end='') num1 += 1 print() num2 += 1
for循环
1.基本语法
for i in range(3): print (i) range(3) [0,1,2] range(1,3) [1,2]
i 相当于临时变量
将 [0,1,2] 依次赋值给临时变量 i
# 方法1: for i in range(100): if i % 2 == 1: print (i) # 方法2: for i in range(1,101): if i % 2 != 0: print (i) # 方法3: for i in range(1,101,2): print (i)
_user = 'alex' _passwd = 'abc123' passed_authentication = False # flag = 标志位 for i in range(3): username = input('Username:') password = input('Password:') if username == _user and password == _passwd: print ('Welcome %s login...' %_user) passed_authentication = True break # 中断,跳出当前循环 else: print('Invalid username or password!') if not passed_authentication: print('您的用户已被锁定!')
_user = 'alex' _passwd = 'abc123' passed_authentication = False # flag = 标志位 for i in range(3): username = input('Username:') password = input('Password:') if username == _user and password == _passwd: print ('Welcome %s login...' %_user) break # 中断,跳出当前循环 else: print('Invalid username or password!') else: # 只要上面的for循环正常执行完毕,中间没被打断,就会执行else语句 print('您的用户已被锁定!')
2.循环中的contitnue与break
for i in range(10): if i < 5: continue #结束本次循环,继续下一次循环 print (i) for j in range(10): print('layer2:',j) if j == 6: break #中断、跳出当前循环
3.标志位介绍
xit_flag = False #设置标志位 for i in range(10): if i < 5: continue #结束本次循环,继续下一次循环 print (i) for j in range(10): print('layer2:',j) if j == 6: exit_flag = True #通过设置标志位,当内层循环中断时,外层循环也中断 break if exit_flag: break