yield生成器及字符串的格式化

一、生成器

 def ran():
     print('Hello world')
     yield 'F1'

     print('Hey there!')
     yield 'F2'

     print('goodbye')
     yield 'F3'

 ret = ran() # ran()称为生成器函数，ret才是生成器，仅仅具有一种生成能力，函数内部要有关键字yield
 print(ret)

 res = ret.__next__() #对生成器进行循环操作，遇到yield会停止操作，将yield的值返回给变量，并会记录保存位置
 print(res)

 res1 = ret.__next__() #下次再对生成器进行操作，会从停止出开始，直到下一个yield停止
 print(res1) # 当__next__次数超过yield时，会报错

 for i in ret: #进行__next__之后再进行for循环，也是从上次yield停止处开始
     print(i)

二、字符串的格式化

① % 方法

 s = 'I am a %s guy' % ('good')
 print(s)

 n = 'I am a %s guy,%d years old' % ('good',28)
 print(n)

 d = 'I am a %(n1)s guy,%(n2)d years old' % {'n1':"good",'n2':28}
 print(d)

 f = 'I am %f' % (28) # 浮点数占位符，默认保留小数点后6位，四舍五入
 print(f)

 f1 = 'I am %.2f' % (28) #设置保留小数点后2位
 print(f1)

 # typecode
 %s : 字符串
 %d : 十进制数字
 %f ：浮点型
 %% ：%
 %o : 将十进制转换成八进制返回
 %x ：将十进制转换成十六进制返回
 %e ：将数字转换成科学记数法

② format方法

 tem = 'I am {},age {},'.format('Ethan',28)
 print(tem)

 tem = 'I am {},age {},{}'.format(*['Ethan',28,'Ethan'])
 print(tem)

 tem = 'I am {0},age {1},really {0}'.format('Ethan',28)
 print(tem)

 tem = 'I am {0},age {1},really {0}'.format(*['Ethan',28])
 print(tem)

 tem = 'I am {name},age {age},really {name}'.format(**{'name':'Ethan',"age":28})
 print(tem)

 tem = 'I am {name},age {age},really {name}'.format(name = 'Ethan',age = 28)
 print(tem)

 tem = 'I am {0[0]},age {0[1]},really {0[0]}'.format(['Ethan',28],['Seven',27])
 print(tem)

 tem = 'I am {:s},age {:d},money {:f}'.format('Ethan',28,8988.23)
 print(tem) # I am Ethan,age 28,money 8988.230000

 tem = 'I am {:s},age {:d}'.format(*['Ethan',28])
 print(tem)

 tem = 'I am {name:s},age {age:d}'.format(age = 28,name = 'Ethan')
 print(tem)

 tem = 'I am {name:s},age {age:d}'.format(**{'name':'Ethan','age':28})
 print(tem)

 tem = 'Numbers:{:b},{:o},{:d},{:x},{:X},{:%}'.format(15,15,15,15,15,15.87623,2)
 print(tem) # Numbers:1111,17,15,f,F,1587.623000%