python-for循环-数字类型-字符串类型str

文章目录

一、for循环
二、数字类型
三、字符串类型str

一、for循环

while循环 vs for 循环

while循环：称之为条件循环，循环的次数取决于条件何时为False

for循环：称之为迭代循环，循环的次数取决于数据的包含的元素的个数

for循环专用来取值，在循环取值方面比while循环要强大，以后但凡遇到循环取值的场景，就应该用for循环

l=['a','b','c']
for i in range(3):print(i,l[i])

#for+break
names=['egon','kevin','alex','hulaoshi']
for name in names:if name == 'alex':breakprint(name)

#for+continue
names=['egon','kevin','alex','hulaoshi']
for name in names:if name == 'alex':continueprint(name)

#for+else
names=['egon','kevin','alex','hulaoshi']
for name in names:print(name)
else:print('=====>')

#for循环嵌套
for i in range(3):for j in range(2):print(i,j)
"""
外层循环第一次：i=0内层循环0，00，1
外层循环第二次：i=1内层循环1，01，1
外层循环第三次：i=2内层循环2，02，1"""

二、数字类型

整型int

用途：记录年龄、等级、号码等

定义方式：

age = 10 #age = int(10)

类型转换

print(int(3.1)) #结果3
res = (int('11'))
print(res,type(res)) #结果11，类型intres = (float('11.1'))
print(res,type(res)) #结果11.1，类型float

了解

print(bin(12)) #10进制转2进制
print(oct(12)) #10进制转8进制
print(hex(12)) #10进制转16进制

存一个值，不可变

#不可变
x = 10
print(id(x)) #id为1654681344
x = 11
print(id(x)) #id为1654681376

浮点型float

用途：记录身高、体重、薪资等

定义方式

salary = 10.1 # salary = float(10.1)

类型转换

print(float(10)) #结果为10.0
print(float(1.1)) #结果为1.1
print(float('1.1')) #结果为1.1

存一个值，不可变

#不可变
x = 10.3
print(id(x)) #id为2114155192440
x = 11.2
print(id(x)) #id为2114155192512

三、字符串类型str

用途：记录描述型值的状态，比如名字、性别等

定义方式

msg = 'hello world' #msg = str('hello world')

类型转换：可以把任意类型转成字符串类型

res1 = str(10)
res2 = str(10.3)
res3 = str([1, 2, 3])
res4 = str({'x': 1})
print(type(res1))
print(type(res2))
print(type(res3))
print(type(res4))

常用操作+内置方法

优先掌握的操作

按索引取值(正向取+反向取) 只能取

msg = 'hello world'
print(msg[0]) #h
print(msg[-1]) #d

切片(顾头不顾尾，步长)

msg = 'hello world'
print(msg[0:5]) #hello
print(msg[0:5:2]) #hlo
print(msg[0:]) #hello world
print(msg[:]) #hello world
print(msg[-1:-5:-1]) #dlro
print(msg[::-1]) #dlrow olleh

长度len：统计的是字符的个数
```
msg = 'hello world'
print(len(msg)) #11
```
成员运算in和not in：判断一个子字符串是否存在与一个大字符串中
```
msg = 'hello world'
print('ho' in msg) #False
print('ho' not in msg) #True
```

移除空白strip：移除字符串左右两边的某些字符串

msg = '      hello      '
print(msg.strip())msg = '***h**ello**********'
print(msg.strip('*')) #h**ellomsg = '*-=+h/ello*(_+__'
print(msg.strip('*-=+/(_')) #h/ello#示范
name = input('name>>>: ').strip()
pwd = input('password>>>: ').strip()
if name == 'egon' and pwd == '123':print('login successfull')
else:print('username or password error')

切片split:把有规律的字符串切成列表从而方便取值

info = 'egon:18:180:150'
res = info.split(':', 1) #1代表切分机次
print(res) #['egon', '18:180:150']
print(res[1]) #18:180:150info = 'egon:18:180:150'
res = info.split(':')
print(res) #['egon', '18', '180', '150']info = 'egon:18:180:150'
res = info.split(':')
s1=''
for item in res:s1+=item
print(s1) #egon18180150info = 'egon:18:180:150'
res = info.split(':')
s1 = ':'.join(res)
print(s1) # egon:18:180:150

循环
```
for i in 'hello':print(i)
```

需要掌握的操作

strip,lstrip,rstrip

msg = '*****hello****'
print(msg.strip('*')) #hello
print(msg.lstrip('*')) #hello****
print(msg.rstrip('*')) #*****hello

lower,upper

msg = 'AaBbCc123123123'
print(msg.lower()) #aabbcc123123123
print(msg.upper()) #AABBCC123123123

startswith,endswith

msg = 'alex is dsb'
print(msg.startswith('alex')) #True
print(msg.endswith('sb')) #True

format的三种玩法

msg = 'my name is {name} my age is {age}'.format(age=18, name='egon')
print(msg) #my name is egon my age is 18msg = 'my name is {} my age is {}'.format(18, 'egon')
print(msg) #my name is 18 my age is egonmsg = 'my name is {0}{0} my age is {1}{1}{1}'.format(18, 'egon')
print(msg) #my name is 1818 my age is egonegonegon

split,rsplit

cmd = 'get|a.txt|33333'
print(cmd.split('|', 1)) #['get', 'a.txt|33333']
print(cmd.rsplit('|', 1)) #['get|a.txt', '33333']

replace

msg = 'kevin is sb kevin kevin'
print(msg.replace('kevin', 'sb', 2)) #sb is sb sb kevin

isdigit #当字符串内为纯数字时结果为True

res = '11111'
print(res.isdigit())
int(res) #True#示范
age_of_bk = 18
inp_age = input('your age: ').strip()
if inp_age.isdigit():inp_age = int(inp_age)if inp_age > 18:print('too big')elif inp_age < 18:print('to small')else:print('you got it')
else:print('必须输入纯数字')

了解

find,rfind,index,rindex,count

print('xxxkevin is sb kevin'.find('kevin')) #3
print('xxxkevin is sb kevin'.index('kevin')) #3
print('xxxkevin is sb kevin'.rfind('kevin')) #15
print('xxxkevin is sb kevin'.rindex('kevin')) #15res = 'xxxkevin is sb kevin'.find('kevasdfsadfin')
print(res) #-1 表示没找到
res = 'xxxkevin is sb kevin'.index('kevasdfsadfin')
print(res) #没找到会报错print('kevin is kevin is kevin is sb'.count('kevin')) #3次

center,ljust,rjust,zfill

print('egon'.center(10,'*')) #***egon***
print('egon'.ljust(10,'*')) #egon******
print('egon'.rjust(10,'*')) #******egon
print('egon'.zfill(10)) #000000egon

captalize,swapcase,title

print('my name is kevin'.capitalize()) #My name is kevin
print('AaBbCc'.swapcase()) #aAbBcC
print('my name is kevin'.title()) #My Name Is Kevin

is其他

name = 'egon123'
print(name.isalnum())  # True 字符串由字母或数字组成
print(name.isalpha())  # False 字符串只由字母组成
print(name.islower()) #True
print(name.isupper()) #Falsename = '    '
print(name.isspace()) #Truemsg = 'I Am Egon'
print(msg.istitle()) #True