一、if判斷
模擬人對某些事物的判斷並作出不同的決策的能力。計算機由於要像人一樣的去工作，那么它必須也要具備判斷事物對錯的能力，從而作出不同的響應。實際中的例子，面前走過一個妹紙，你會想好不好看，要不要超過去看看正臉等等。程序中比如ATM取款機，需要接收你輸入的用戶名和密碼來判斷你是否是合法用戶等等。
語法： if 條件：
代碼1
代碼2
代碼3
...
else:
代碼1
代碼2
代碼3
...
if...else...表示代碼成立會怎么樣，else表示不成立會怎么樣。
cls = 'human' gender = 'female' age = 18 if cls == 'human'and 'gender' == 'female' and age >16 and age < 22: print('上去表白') else： print(‘打擾了’')
if...elif...
if 條件1:
代碼1
代碼2
代碼3
...
elif 條件2:
代碼1
代碼2
代碼3
...
elif 條件3:
代碼1
代碼2
代碼3
...
...
else:
代碼1
代碼2
代碼3
...
if...elif...else表示if條件1成立干什么，elif條件2成立干什么，elif條件3成立干什么，elif...否則干什么。
if...elif...else
cls = 'human'
gender = 'female'
age = 28
if cls == 'human' and gender == 'female' and age > 16 and age < 22:
print('開始表白')
elif cls == 'human' and gender == 'female' and age > 22 and age < 30:
print('考慮下')
else:
print('阿姨好')
應用實例：#模擬注冊登錄
user_name = 'zzj'
user_pwd = '123'
inp_name = input('please input your name>>>:')
inp_pwd = input('please input your password>>>:')
if user_name == inp_name and userpwd == inp_pwd:
print('登陸成功！')
else :
print('登錄錯誤！')
#一周安排
print('''必須輸入其中一種:
Monday
Tuesday
Wednesday
Thursday
Friday
Saturday Sunday
''')
today=input('>>: ')
if today == 'Monday' or today == 'Tuesday' or today == 'Wednesday' or today == 'Thursday' or today == 'Friday':
print('上班')
elif today == 'Saturday' or today == 'Sunday':
print('出去浪')
else:
print('''必須輸入其中一種:
Monday
Tuesday
Wednesday
Thursday
Friday
Saturday
Sunday
''')
if 的嵌套
cls = 'human'
gender = 'female'
age = 18
is_success = False
if cls == 'human' and gender == 'female' and age > 16 and age < 22:
print('開始表白')
if is_success:
print('那我們一起走吧...')
else:
print('我逗你玩呢')
else:
print('阿姨好')
二、while循環
實現ATM的輸入密碼重新輸入的功能
user_db = 'nick'
pwd_db = ‘123’
while True:
inp_user = input('username:')
inp_pwd = input('password:')
if inp_user == user_db and pwd_db == inp_pwd:
print('login successful')
else:
print('username or password error')
while + break
break 的意思就是終止掉當前層的循環，執行其他代碼。
#break 語句演示
while True :
print('1')
print('2')
print('3')
break
例：
user_db = 'jason'
pwd_db = '123'
while True:
inp_user = input('username: ')
inp_pwd = input('password: ')
if inp_user == user_db and pwd_db == inp_pwd:
print('login successful')
break
else:
print('username or password error')
print('退出了while循環')
#while + else
n = 1
while n < 3:
if n == 2:
print(n)
n +=1
else:
ptint('else會在while沒有break時才會執行else中的代碼')
三、for 循環
1. for i in range(1,10): #range顧頭不顧尾
print(i)
2.name_list = ['jason','zzj','angela']
for i in range(len(name_list)):
prtint(i,name_list[i])
3.for + break 跳出本層循環
name = ['jason','zzj','angela']
for i in name:
if i == 'zzj':
break
print(i)
4.for + continue
name = ['jason','zzj','angela']
for i in name:
if i == 'zzj':
continue
print(i)
5.for循環練習題
打印九九乘法口訣表
for i in range(1,10): for j in range(1,i+1): print('%s*%s=%s'%(i,j,i*j),end=' ') print()