Python 执行字符串表达式函数(eval exec execfile)

Python 2.7.2 (default, Jun 12 2011, 15:08:59) [MSC v.1500 32 bit (Intel)] on win32
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> x=1
> print eval("x+1")
2
> exec "print 'http://blog.leniy.org/python-eval-exec-execfile.html'"
http://blog.leniy.org/python-eval-exec-execfile.html
> 

> input("请输入:")
请输入:1+2**3
9
> 

> eval(raw_input("请输入:"))
请输入:1+2**3
9
>