常量:
Python中常以大写的变量名来标注常量。
算数运算符补充:
10/3(除法)
10//3(除法取整数部分)
10**2(次方)
赋值运算:
增量赋值
age+=1(age=age+1)
age/=3(age=age/3)
age**=2(age=age**2)
交叉赋值:
x=10 y=20 x,y=y,x #temp=x #x=y #y=temp print(x,y)
链式赋值
x=y=z=10
解压赋值
l=[1.2,2,3,4.4,5] a,b,c,d,e=l print(a,b,c,d,e) a,b,*_=l print(a,b)
if判断
语法一:
if 条件:
代码1
代码2
代码3
...
age_of_bk=30 print('start.....') inp_age=input('>>>:') inp_age=int(inp_age) if inp_age==age_of_bk print('猜对了') print('猜对了') print('end')
语法二:
if 条件:
代码1
代码2
代码3
....
else
代码1
代码2
代码3
....
age=38 gender='male' is_beautiful=True if age>=18 and age <=25 and gender='male' and is_beautiful print('开始表白') else: print('阿姨好')
语法三
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
....
score=input('your score>>:') 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')
语法4:
if 条件1:
if 条件2:
代码1
代码2
代码3
...
代码2
代码3
age=18 gender='female' is_beautiful=True is_successful=True if age >= 18 and age <= 25 and gender == 'female' and is_beautiful: print('开始表白。。。。') if is_successful: print('在一起') else: print('我逗你玩呢。。。') else: print('阿姨好')
while循环:条件循环
while 条件:
代码1
代码2
代码3
...
name_of_bk='egon' pwd_of_bk='123' tag=True while tag: inp_name=input('your name>>: ') inp_pwd=input('your password>>: ') if inp_name == name_of_bk and inp_pwd == pwd_of_bk: print('login successful') tag=False else: print('username or password error') print('other code...')
while+break:break代表结束本层循环
while True:
print(1)
break
print(2)
print(3)
name_of_bk='egon' pwd_of_bk='123' while True: inp_name=input('your name>>: ') inp_pwd=input('your password>>: ') if inp_name == name_of_bk and inp_pwd == pwd_of_bk: print('login successful') break else: print('username or password error') print('other code......')
while + continue: continue代表结束本次循环,直接进入下一次
count=1 while count < 6: if count == 3: count+=1 continue print(count) count+=1
while + else
count=0 while count <= 10: print(count) count+=1 else: print("else的子代块只有在while循环没有被break打断的情况下才会执行")
name_of_bk='egon' pwd_of_bk='123' count=0 tag=True while tag: if count == 3: print('输错的次数过多。。。') break inp_name=input('your name>>: ') inp_pwd=input('your password>>: ') if inp_name == name_of_bk and inp_pwd == pwd_of_bk: print('login successful') while tag: print(""" 0 退出 1 购物 2 支付 3 查看购物 """) cmd=input('>>>: ') if cmd == '0': tag=False continue if cmd == '1': print('购物。。。。。。。') elif cmd == '2': print('支付。。。。。') elif cmd == '3': print('查看购物车') else: print('输入错误的指令') else: print('username or password error') count+=1 #count=3 输错3次
for循环
l=['a','b','c'] print(len(l)) i=0 while i<len(l): print(l[i]) i+=1 #while循环 l=['a','b','c'] for item in l: print(item) #for循环 dic={'x':111,'y':222,'z':333} for k in dic:#k='x' print(k,dic[k])
while循环 VS for循环
1.
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:称之为迭代器循环,循环的次数取决于数据的包含的元素的个数
2.
for循环专门用来取值,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
# for+break # names=['egon','kevin','alex','hulaoshi'] # for name in names: # if name == 'alex':break # print(name) # for+continue # names=['egon','kevin','alex','hulaoshi'] # for name in names: # if name == 'alex':continue # print(name) # for+else # names=['egon','kevin','alex','hulaoshi'] # for name in names: # # if name == 'alex':break # print(name) # else: # print('=====>') # for循环嵌套 # for i in range(3): #i=2 # for j in range(2): #j=1 # print(i,j) #2,1