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Python学习笔记Day4

程序员文章站 2022-04-14 17:02:40
今日学习内容 1、if 判断(流程控制的一种) 2、while循环(条件循环) 3、for循环(迭代器循环) 一、if 判断 语法一:if判断 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“ ......

今日学习内容

                  1、if 判断(流程控制的一种)

                  2、while循环(条件循环)

                  3、for循环(迭代器循环)

==========================================================

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:

Python学习笔记Day4
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
Python学习笔记Day4
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
Python学习笔记Day4
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
'''