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%