exec 和 eval

exec

exec语句用来执行储存在字符串或文件中的Python语句, 我们可以运行一个包含Python语句的字符串

>>> exec "print 'Hello Python'"
Hello Python

但是exec可能会干扰Python语句的命名空间, 从而影响到原来的函数运行

>>> from math import sqrt
>>> exec "sqrt = 1"
>>> sqrt(4)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'int' object is not callable

解决方案:

>>> from math import sqrt
>>> temp = {}
>>> exec "sqrt = 1" in temp
>>> sqrt(4)
2.0
>>> temp['sqrt']
1

eval

---

>>> eval(raw_input('input two number: '))
input two number: 2+3*5
17