条件判断 if
语法一： if 条件: # 条件成立时执行的子代码块 代码1 代码2 代码3
示例：sex='female'age=18is_beautiful=Trueif sex == 'female' and age > 16 and age < 20 and is_beautiful: print('开始表白。。。')print('other code1...')print('other code2...')print('other code3...') 语法二： if 条件: # 条件成立时执行的子代码块 代码1 代码2 代码3 else: # 条件不成立时执行的子代码块 代码1 代码2 代码3
示例：sex='female'age=38is_beautiful=Trueif sex == 'female' and age > 16 and age < 20 and is_beautiful: print('开始表白。。。')else: print('阿姨好。。。')print('other code1...')print('other code2...')print('other code3...') 语法三： if 条件1: if 条件2: 代码1 代码2 代码3
示例：sex='female'age=18is_beautiful=Trueis_successful=Trueheight=1.70if sex == 'female' and age > 16 and age < 20 and is_beautiful \ and height > 1.60 and height < 1.80: print('开始表白。。。') if is_successful: print('在一起。。。') else: print('什么爱情不爱情的,爱nmlgb的爱情,爱nmlg啊.')else: print('阿姨好。。。')print('other code1...')print('other code2...')print('other code3...') 语法四： if 条件1: 代码1 代码2 代码3 elif 条件2: 代码1 代码2 代码3 elif 条件3: 代码1 代码2 代码3 ....... else: 代码1 代码2 代码3
示例：如果成绩 >= 90，那么：优秀如果成绩 >= 80且 < 90, 那么：良好 如果成绩 >= 70且 < 80, 那么：普通其他情况：很差score = input('please input your score: ') # score='100'score = int(score)if score >= 90: print('优秀')elif score >= 80: print('良好')elif score >= 70: print('普通')else: print('很差') 流程控制：while循环
语法： while 条件: 代码1 代码2 代码3
while True: name=input('please input your name: ') pwd=input('please input your password: ') if name == 'egon' and pwd == '123': print('login successful') else: print('username or password error') 结束while循环的两种方式 方式一：条件改为False， 在条件改为False时不会立即结束掉循环，而是要等到下一次循环判断条件时才会生效
tag=True while tag: name=input('please input your name: ') pwd=input('please input your password: ') if name == 'egon' and pwd == '123': print('login successful') tag=False else: print('username or password error') print('===>') 方式二：while+break break一定要放在循环体内，一旦循环体执行到break就会立即结束本层循环
while True: name=input('please input your name: ') pwd=input('please input your password: ') if name == 'egon' and pwd == '123': print('login successful') break else: print('username or password error') print('===>>>>>') print('===>>>>>') while+continue:结束本次循环，直接进入下一次循环
示例一count=1while count < 6: #count=6 if count == 4: count += 1 continue print(count) count+=1
示例二：while True: name=input('please input your name: ') pwd=input('please input your password: ') if name == 'egon' and pwd == '123': print('login successful') break else: print('username or password error') # continue # 此处加continue无用 了解知识 while + else: while 条件: 代码1 代码2 代码3 else: 在循环结束后，并且在循环没有被break打断过的情况下，才会执行else的代码
tag=Truewhile tag: print(1) print(2) print(3) # tag=False breakelse: print('else的代码') while 条件1:
while 条件2:
代码1 代码2 代码3示范一：while True: name=input('please input your name: ') pwd=input('please input your password: ') if name == 'egon' and pwd == '123': print('login successful') while True: print(""" 0 退出 1 取款 2 转账 3 查询 """) choice=input('请输入您要执行的操作：') #choice='1' if choice == '0': break elif choice == '1': print('取款。。。') elif choice == '2': print('转账。。。') elif choice == '3': print('查询') else: print('输入指令错误，请重新输入') break else: print('username or password error') 示范二：tag=Truewhile tag: name=input('please input your name: ') pwd=input('please input your password: ') if name == 'egon' and pwd == '123': print('login successful') while tag: print(""" 0 退出 1 取款 2 转账 3 查询 """) choice=input('请输入您要执行的操作：') #choice='1' if choice == '0': tag=False elif choice == '1': print('取款。。。') elif choice == '2': print('转账。。。') elif choice == '3': print('查询') else: print('输入指令错误，请重新输入') else: print('username or password error') 流程控制：for循环
for循环的强大之处在于循环取值
l=['a','b','c','d','e']i=0while i < len(l): print(l[i]) i+=1for x in l: # x='b' print(x)dic={ 'name':'egon','age':18,'gender':'male'}for x in dic: print(x,dic[x]) for + break
nums=[11,22,33,44,55]for x in nums: if x == 44: break print(x)
for + continue
nums=[11,22,33,44,55]for x in nums: if x == 22 or x == 44: continue print(x)
for + else
names=['egon','kevin1111_dsb','alex_dsb','mac_dsb']for name in names: if name == 'kevin_dsb': break print(name)else: print('======>') for+ range()
range的用法>>> range(1,5)[1, 2, 3, 4]>>> for i in range(1,5):... print(i)...1234>>> range(1,5,1)[1, 2, 3, 4]>>> range(1,5,2) # 1 3[1, 3]
for i in range(5): # 0 1 2 3 4 print(i)
for嵌套
for嵌套for i in range(3): for j in range(4): print(i,j)执行结果：0 00 10 20 31 01 11 21 32 02 12 22 3