exec 关键字在 python 中有什么作用? [英] what does the exec keyword do in python?

问题描述

code = compile('a = 1 + 2', '', 'exec')执行代码打印一个3

它是如何打印 3 的?有人能告诉我它的确切工作原理吗?

解决方案

因此 exec 语句可用于执行存储在字符串中的代码.这允许您将代码存储在字符串中.自然地，所有对字符串有效的操作都可以完成.如下所示:

注意:exec是python 2.7x上的语句，3.x上的函数

随机导入statement = 'print "%s"%(random.random());执行语句

输出:

<预><代码>>>>运行文件(...)0.215359778598>>>运行文件(...)0.702406617438>>>运行文件(...)0.455131491306

另见:eval、exec 和编译

它可以在测试复杂的数学函数时派上用场.例如:

定义 someMath(n,m,r):return (n**m)//r

随机导入test = 'print "结果为:", someMath(random.random(),random.random(),random.random())'对于范围内的我(20):执行测试

输出:

结果是:1.0结果是:70.0结果是:1.0结果是:2.0结果是:1.0结果是:1.0结果是:0.0结果是:11.0...

code = compile('a = 1 + 2', '<string>', 'exec')
exec code
print a
3

How it prints 3?, Can anybody tell me the exact working of it?

解决方案

So the exec statement can be used to execute code stored in strings. This allows you to store code in strings. Naturally all manipulations that are valid on strings can be done. This is demonstrated below:

Note: exec is a statement in python 2.7x and a function on 3.x

import random
statement = 'print "%s"%(random.random());
exec statement

Output:

>>> runfile(...)
0.215359778598
>>> runfile(...)
0.702406617438
>>> runfile(...)
0.455131491306

See also: Difference between eval, exec and compile

It can come in pretty handy while testing complex math functions. For instance:

def someMath(n,m,r): return (n**m)//r

import random
test = 'print "The result of is: ", someMath(random.random(),random.random(),random.random())'
for i in range(20):
    exec test

Output:

The result of is : 1.0
The result of is :  70.0
The result of is :  1.0
The result of is :  2.0
The result of is :  1.0
The result of is :  1.0
The result of is :  0.0
The result of is :  11.0
...

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