《Python核心编程》P21输入数值字符串→转整型

>>> num=input(‘n:‘)
n:1234
>>> print(‘sdf:‘,n)
Traceback (most recent call last):
  File "<pyshell#72>", line 1, in <module>
    print(‘sdf:‘,n)
NameError: name ‘n‘ is not defined
>>> print(‘sdf:‘,num)
sdf: 1234
>>> print(‘sdf:‘,int(num))
sdf: 1234
>>> print(‘sdf:‘,int(num)*2)
sdf: 2468
>>> print(‘sdf:%d‘,int(num)*2)     #前有%d，后用的逗号，没用%：%d当做字符输出了
sdf:%d 2468
>>> print(‘sdf:%d‘%int(num)*2)
sdf:1234sdf:1234
>>> print(‘sdf:%d‘%int((num)*2)))
SyntaxError: invalid syntax
>>> print(‘sdf:%d‘%(int((num)*2)))
sdf:12341234
>>> print(‘sdf:%d‘%(int(num)*2))
sdf:2468
>>> 
>>> print(‘sdf:‘%int(num)*2)      #后面有% 没用逗号，而前面没有%，错误
Traceback (most recent call last):
  File "<pyshell#84>", line 1, in <module>
    print(‘sdf:‘%int(num)*2)
TypeError: not all arguments converted during string formatting
>>> print(‘sdf:‘%(int(num)*2))
Traceback (most recent call last):
  File "<pyshell#85>", line 1, in <module>
    print(‘sdf:‘%(int(num)*2))
TypeError: not all arguments converted during string formatting
>>>