在字符串中引入变量有三种方法：
1、+ 连字符
name = 'zhangsan'
print('my name is '+name)结果为
my name is zhangsan
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2、% 字符
name = 'zhangsan'
age = 25
price = 4500.225
print('my name is %s'%(name))
print('i am %d'%(age)+' years old')
print('my price is %f'%(price))
#保留指定位数小数(四舍五入)
print('my price is %.2f'%(price))结果为
my name is zhangsan i am 25 years old my price is 4500.225000 my price is 4500.23
3、format()函数
对于变量较多的情况，使用'+'或者'%'相对比较麻烦，这种情况下可以使用format函数
name = 'zhangsan'
age = 25
price = 4500.225
info = 'my name is {my_name},i am {my_age} years old,my price is {my_price}'\
.format(my_name=name,my_age=age,my_price=price)
print(info)结果为：
my name is zhangsan,i am 25 years old,my price is 4500.225
