今日学习内容
1、if 判断(流程控制的一种)
写重复的代码是程序员最不耻的行为,所以我们需要while循环和for循环 ,^_^!
2、while循环(条件循环)
3、for循环(迭代器循环)
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一、if 判断
语法一:if判断
sex = 'female'
age = 32
is_beautiful = True
if sex == 'female' and age == 18 and is_beautiful:
print('Begin your love words:')
print('another code1')
print('another code2')
if判断使用注意事项:if条件紧跟着一个冒号:+回车,pycharm会自动进入到下一行并缩进4个空格,开始进入运行一组代码块。在这里注意中英文输入法对代码“括号、冒号、逗号”这些字符的影响,谨记一定要用英文输入法输入,不然容易出现报错。
语法二:if+else判断
sex = 'female'
age = 18
is_beautiful = True
if sex == 'female' and 16 < age <24 and is_beautiful:
print('Begin your love words.')
else:
print('Say nothing...')
语法三:if+else 的嵌套
sex = 'female'
age = 18
is_beautiful = True
is_success = True
if sex == 'female' and 16 < age <24 and is_beautiful:
print('Begin your love words.')
if is_success:
print('HaHaHa')
else:
print('I hate love,go away!')
else:
print('Say nothing...')
tip:①and 多个条件并过长时,可用‘\+回车’来多行显示,这里不影响语法。
②快捷操作,TAB键 可以进行快捷缩进,比如选中多行一起快捷缩进,要回退的话,按shift+tab组合键。
语法四:if+elif+else
# 输入成绩判断优秀、很好、一般、很差
score = input('Please input your score:')
score = int(score)
if score >= 90:
print('优秀')
elif score >= 80:
print('很好')
elif score >= 70:
print('一般')
else:
print('很差')
小练习:
name = input('请输入您的用户名:')
pwd = input('请输入您的密码:')
if name == 'sgt' and pwd == '123':
print('登陆成功')
else:
print('用户名或密码错误')
练习一:用户登陆验证
sgt = 'spueradministrator'
sgf = 'systemadministrator'
shr = 'administrator'
sqs = 'guest'
name = input('please input your username:')
if name == 'sgt':
print('你好,超级管理员!')
elif name =='sgf':
print('你好,系统管理员!')
elif name == 'shr':
print('你好,管理员!')
elif name == 'sqs':
print('你好,宾客!')
根据用户输入内容打印其权限
while True:
today = input('今天是星期几?')
if today == 'monday' or today == 'tuesday' or today == 'wednesday'\
or today == 'thursday' or today == 'friday':
print('上班')
break
elif today == 'saturday' or today == 'sunday':
print('出去浪')
break
else:
print('''
必须输入以下任意一种:
monday
tuesday
wednesday
thursday
friday
saturday
sunday
''')
上班或出去浪
二、while循环
方式一:while+True/False
tag = True
while tag:
name = input('please input your name:')
pwd = input('please input your password:')
if name == 'sgt' and pwd == '123':
print('congratulation,region success!')
tag = False
else:
print('your name or password is wrong,please try again!')
方法二:while+break
while True:
name = input('please input your name:')
pwd = input('please input your password:')
if name == 'sgt' and pwd == '123':
print('congratulation,region success!')
break
else:
print('your name or password is wrong,please try again!')
break是终止本层while循环。
方法三:while+continue
nums = 1
while nums <= 6:
if nums == 4 or nums == 5:
nums += 1
continue
else:
print(nums)
nums += 1
终止当前循环,直接进入下次循环。
方法四:while+else
nums = 1
while nums <= 6:
if nums == 4 or nums == 5:
nums += 1
continue
else:
print(nums)
nums += 1
else:
print('前面代码无break,else 条件成立,否则else不执行。')
方法五:while的嵌套
示例一:
while True:
name = input('please input your username:')
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:')
if choice == '0':
break
elif choice == '1':
print('取款...')
elif choice == '2':
print('转账...')
elif choice == '3':
print('查询...')
else:
print('输入指令有误,请重新输入:')
break
else:
print('username or password error!')
改进示例二:
tag = True
while tag:
name = input('please input your username:')
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('请输入您要执行的代码:')
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('指令错误,请重新输入')
else:
print('username or password error')
三、for 循环 (其强大之处在于循环取值)
方案一、
for循环取值列表:
取值如果用while循环:
l = ['a', 'b', 'c', 'd', 'e']
i = 0
while i < len(l): #这里的len(l)表示计算列表l的长度(也就是索
#引数)
print(l[i])
i += 1
如果我们使用for循环取值:
l = ['a', 'b', 'c', 'd', 'e']
for x in l: #这里的x in l 是直接将l列表里的数据取出关联
print(x) #到x,不用额外赋值。
for循环取值字典:
info = {'sgt': 'me', 'sgf': 'brother', 'age': 18, 'sun': 'shr'}
for x in info:
print(x, info[x])
方案二、for+break
取出列表前几个数,后面的不取
nums = [11, 22, 33, 44, 55]
for x in nums:
if x == 44:
break
print(x)
方案三、for+continue
不取其中的多个数据
nums = [11, 22, 33, 44, 55]
for x in nums:
if x == 22 or x == 44:
continue
print(x)
方案四、for+else
names = ['egon', 'alexdsb', 'sb', 'dsb']
for name in names:
if name == 'alexdsb':
break
print(name)
else:
print('>>>>>>>>>>>')
#有break ,else下面的print不执行。
names = ['egon', 'alexdsb', 'sb', 'dsb']
for name in names:
if name == 'alexdsb':
continue
print(name)
else:
print('>>>>>>>>>>>')
#如果无break,else下面的print执行。
方案五、for+range()
range的用法:
>>> range(5)
[0, 1, 2, 3, 4]
>>> range(1,5)
[1, 2, 3, 4]
>>> range(1,5,2)
[1, 3]
>>> range(1,1)
[]
>>>
正规格式为range(1,5,2)
表示:从1开始计数,每计数一次递增2,所以结果是[1,3]
如果括号里只有一个数,代表(0,5,1),即从0开始计数,递增数为1.
示例:
for x in range(5):
print(x)
#结果:
#0
#1
#2
#3
#4
方案六、for循环嵌套
for x in range(3):
for y in range(3):
print(x, y)
'''
结果
0 0
0 1
0 2
1 0
1 1
1 2
2 0
2 1
2 2
'''